Summary. Blood samples were collected from 13 roebucks 1 to 3 times per month during several years to study the relationship between season and concentrations of LH, FSH, testosterone and prolactin. Plasma values of all of these hormones began to increase during the second half of February. LH, FSH and testosterone levels reached a plateau during April. Highest average levels of LH and testosterone were observed before the start of the rutting season (mid-July—mid-August) and steadily declined thereafter. In contrast to LH and testosterone, FSH concentrations decreased 6 weeks earlier, during June, indicating a modulated secretion pattern. Prolactin steadily increased until the beginning of July and then decreased.
Christiane Menzer and D. Schams
Summary. A double-antibody radioimmunoassay for PMSG, especially for measuring PMSG in cattle blood after exogenous application, has been developed. A rabbit antiserum against PMSG and pure PMSG for radioiodination were used. There was a strong cross-reaction against equine LH and FSH, but the slight cross-reaction against bovine LH and FSH could be eliminated by adding bovine LH to each tube during the assay. Unspecific, interfering influences of equine or cow serum could be eliminated by adding a constant amount of PMSG-free serum to each tube. PMSG added to 200 μl of serum could be recovered by this method with a mean of 90·5 ± 9·9%. Inhibition curves obtained with pregnant mare serum or cow serum after administration of PMSG were parallel to those obtained with the PMSG standard preparation. The intra-assay coefficient of variation (CV) was 6·9%. The inter-assay CV was 12·6%. Sensitivity of the assay was 1 mi.u. PMSG/tube. Values of PMSG measured in the serum of pregnant mares by this assay were comparable with those obtained by a bioassay on the same samples. PMSG was still measurable in blood serum about 10 days after injection of 1500–3000 i.u. PMSG. After infusion of 12 000 i.u. PMSG for 3 h (2 heifers), the half-life of PMSG was found to have two components, one of 51 or 40 h and a slower one of 123 or 118 h.
H. KARG and D. SCHAMS
The cow has been specifically selected for lactational performance. It has no lactational anoestrus and the simultaneous reproductive ability and milk yield have not only scientific interest but economic importance too. We have no evidence of a luteotrophic action of prolactin (Hoffmann, Schams, Bopp, Ender, Giménez & Karg, 1974) in this species such as has been shown in some others. Furthermore, mammary cancer, one motivation for the increasing amount of work devoted to studies on prolactin in man, has not been recorded in the cow.
RADIOIMMUNOASSAY FOR BOVINE PROLACTIN
In 1969, a specific radioimmunoassay for bovine prolactin using NIH-P-B2 (biological activity 19·9 i.u./mg) as antigen was developed (Schams & Karg, 1969). In this system there were no cross reactions with growth hormone or other pituitary hormones.
SPECIFIC INHIBITION OF PROLACTIN RELEASE
It has been shown that some ergot alkaloids have
F. J. Schweigert and D. Schams
During the period of lactational oestrus, the corpus luteum of ovaries of grey seals decreased in size following the birth of the pup, while on the contralateral ovary one major large follicle rapidly expanded. These large follicles had the highest concentration of oestradiol (4282 ± 609 ng ml−1) and progesterone (499 ± 168 ng ml−1). Osmolality (322 ± 3 mosmol kg−1) and the intrafollicular concentration of electrolytes (Na: 126 ± 1; Cl: 96 ± 1; Ca: 1.3 ± 0.1 μmol ml−1) and proteins (94 ± 1 mg ml−1) were independent of stage of lactation and follicle size. Concentrations were lower in follicular fluid than in plasma. The concentrations of triglycerides and, to some extent, those of vitamin E, cholesterol and phospholipids were affected by the decrease in the plasma concentration of these components with the onset of lactation and the increase in follicle size. These two events resulted in a marked decrease of these components in the largest follicles at the end of lactational oestrus. Vitamin A (exclusively as retinol), although a blood-borne component in follicular fluid, was the only component with a higher concentration in small and medium follicles than in plasma and decreased with increasing follicle size despite an increase in plasma retinol. This decrease and the negative correlation with intrafollicular oestradiol might indicate a high demand of preovulatory follicle structures for vitamin A owing to its possible importance in steroid hormone or protein synthesis or in both processes. Changes in the chemical composition of follicular fluid and the morphological findings indicate a continuous development of the dominant follicle throughout the lactational oestrus in grey seals.
D. Schams, D. Barth and H. Karg
Summary. Progesterone, LH and FSH were measured in the plasma of 4 female roe deer (2 kept with the buck, 2 separated from the buck to prevent mating) from July until the end of September or October, i.e. including the rutting season from the middle of July to the middle of August. At least two distinct peaks of LH and FSH were observed before the first small progesterone increase lasting for about 5 days in late July. The next clear LH peak and, with slight individual variations, FSH peak occurred exactly when progesterone values had fallen and before they rose again in a major elevation, i.e. after ovulation. LH and, with some variations, FSH values were generally basal while progesterone was high during the rest of the study. There were no obvious differences in hormone pattern in pregnant and non-pregnant animals.
D. L. Walters, D. Schams and E. Schallenberger
Summary. All hormones were determined in blood samples collected simultaneously from the caudal vena cava and jugular vein at 20-min intervals for 12 h during the early (Day 4) and mid- (~Day 11) luteal phases of the oestrous cycle in 7 cows. Mean concentrations of oestradiol, progesterone and oxytocin were greater (P < 0·01) in the vena cava than in the jugular vein. Pulses of these hormones were also more easily identifiable in the vena cava. The frequency of LH pulses was higher (P < 0·01) during the early luteal than during the mid-luteal phase (8·0 versus 3·6 pulses/12 h). During both phases, 90–96% of all LH pulses were followed within 60 min by a pulse of oestradiol. Basal concentration and amplitude of oestradiol pulses were greater (P < 0·05) during the early than during the mid-luteal phase. The frequency of FSH pulses was similar to that of LH during the early luteal phase (8·5 and 8·0 pulses/12 h) but was greater (P < 0·01) than that of LH during the mid-luteal phase (6·3 versus 3·6 pulses/12 h). Thus, 41% more (P < 0·01) FSH pulses than LH pulses were observed during the mid-luteal phase. However, the separate FSH pulses were associated with low-amplitude short-duration pulses of LH as clarified by an additional study (in 3 cows) using 5-min sampling intervals: 90–100% of all LH/FSH pulses and separate FSH pulses were secreted either concomitantly with or followed by a pulse of progesterone. However, no separate FSH pulses were associated with a pulse of oestradiol. Basal concentration and amplitude of progesterone were greater (P < 0·01) during the mid-luteal than during the early luteal phase. The frequency of oxytocin pulses was similar to that of progesterone during the mid-luteal but not during the early luteal phase. During the mid-luteal phase 97% of all oxytocin pulses were associated with a pulse of progesterone. It is concluded that (1) separate FSH pulses are secreted in addition to parallel LH and FSH pulses during the mid-luteal phase; therefore, the frequency of secretion of LH may be modulated to a greater extent by ovarian steroids than is FSH pulse frequency; (2) pulses of progesterone are probably a result of stimulation by pulses of FSH and/or LH whereas pulses of oestradiol are caused by LH pulses; (3) ovarian oxytocin and progesterone are secreted concomitantly during the mid-luteal phase of the oestrous cycle.
A. Lahlou-Kassi, D. Schams and P. Glatzel
Summary. LH and FSH concentrations were measured during the oestrous cycle in two local Moroccan breeds of sheep with low (Timahdite: 1 CL/cycle) and high (D'man: 3 CL/cycle) ovulation rates. Twenty ewes were used from each breed and blood was collected at 3- or 6-h intervals from 5–4 days before oestrus up to Day 14 of the new cycle, when 4 D'man and 4 Timahdite ewes were ovariectomized. After surgery, blood sampling was continued at 6-h intervals for 2 weeks. (1) The mean basal concentration of LH, the maximum value of the preovulatory LH surge and the area under the curve were significantly higher (P < 0·05) in Timahdite than in D'man ewes. (2) The pattern of FSH in each breed showed no clear basal level but a periodic succession of peaks with variable amplitudes. The first and highest peak corresponded with the preovulatory LH surge. The 2nd peak followed immediately after the first peak and reached its maximum 24–30 h later. The 3rd peak was flatter and occurred around Day 6 of the cycle. The 4th peak was observed around Day 10 of the cycle and showed the lowest amplitude. The 5th and last peak occurred 66–87 h before the next preovulatory surge. (3) FSH concentrations were higher in the prolific D'man than in Timahdite ewes around the time of oestrus (pro-oestrous peak, preovulatory surge and the 2nd peak). The drop in FSH concentrations observed in D'man ewes before the preovulatory surge was more pronounced and started later. (4) After ovariectomy there was a rapid increase in LH and FSH concentrations. The maximum values reached after ovariectomy were similar in the two breeds
D. Schams, E. Schallenberger and J. J. Legros
Summary. In Exp. I, blood samples were collected simultaneously from the posterior vena cava and jugular vein or aorta from 7 heifers every 5–20 min for 2–5 h. Concomitant pulsatile secretion of oxytocin and immunoreactive neurophysin I was detected in the vena cava, but not in the jugular vein or aorta. Concentrations of oxytocin and immunoreactive neurophysin increased earlier and were higher in the vena cava than in the jugular vein or aorta after the injection of a luteolytic dose of prostaglandin F-2α analogue during the mid-luteal phase of the oestrous cycle, demonstrating its ovarian but not pituitary origin. In Exp. II, blood samples were collected from the jugular vein every 12 h during 1 week after oestrus. Follicular growth had been stimulated during the preceding oestrous cycle with PMSG (10 heifers and cows) or with FSH (5 animals); 6 heifers served as controls. There was a high correlation between the number of follicles or CL and the increase in oxytocin and immunoreactive neurophysin I. Although PMSG had a greater luteotrophic effect than did FSH on progesterone secretion, a similar stimulation of oxytocin and immunoreactive neurophysin I was not observed.
It is concluded that immunoreactive neurophysin I and oxytocin are secreted from the ovary in concentrations dependent upon the number of corpora lutea (and of follicles) present. During the mid-luteal period the secretion occurs in a concomitant pulsatile fashion.
E. Schallenberger, D. Schams, B. Bullermann and D. L. Walters
Summary. A luteolytic dose (500 μg) of cloprostenol was given on Day 12 of the oestrous cycle to 5 heifers. Blood samples were collected simultaneously from the caudal vena cava and jugular vein at 5–20-min intervals from – 6 to 0 (control period), 0 to 12 and 24 to 36 h after PG injection. Pulses of LH were secreted concomitantly with pulses of FSH during all sampling periods. However, during the control period separate FSH pulses were detected resulting in a shorter (P < 0·01) interpulse interval for FSH than LH (93 versus 248 min). LH and FSH pulse frequencies increased (P < 0·01) beginning 1–3 h after PG to interpulse intervals of 59 and 63 min, respectively, and continued to be maintained 24–36 h after PG. Concomitantly there was a 2–3-fold increase (P < 0·01) in basal concentrations and pulse amplitude for LH (but not FSH). FSH basal concentrations and pulse amplitudes decreased (P < 0·05) in 3 heifers 24–36 h after PG. Pulsatile secretion of oestradiol was observed at frequencies similar to LH during the periods 4–12 h (3 heifers) and 24–36 h (2 heifers) after PG, respectively, resulting in higher (P < 0·05) mean oestradiol concentrations. Progesterone concentrations in the vena cava increased (P < 0·01) 5–10 min after PG but decreased (P < 0·01) 67% by 20 min after PG. This decrease was followed by a rise (P < 0·05) beginning 2–3 h after PG and lasting for an average of 3·3 h. After a steady decline, basal concentrations of 1·0 ng/ml were reached 24–36 h after PG. Basal oxytocin concentrations in the vena cava and jugular vein (8·2 and 4·2 pg/ml) increased (P < 0·01) to reach maximum concentrations (2029 and 701 pg/ml) 5–10 min after PG and then decreased over a 3–5 h period and were lowest (4–3 and 3–2 pg/ml) 24–36 h after PG. Maximum prolactin concentrations were higher and appeared 5–10 min earlier in the jugular vein compared to the vena cava.
It is concluded that: (1) progesterone and oxytocin secretion from the corpus luteum is initially increased and then dramatically decreased by a luteolytic dose of PG; (2) the reduction of progesterone concentrations below a certain threshold level in the presence of low oestradiol concentrations probably eliminates the negative feedback effect on gonadotrophin secretion, thereby allowing the frequency and amplitude of LH pulses, and to a lesser extent the frequency of FSH pulses, to increase; and (3) the increase in FSH and LH pulse frequencies probably stimulates, after a variable period of time, the development of a large follicle that secretes increasing concentrations of oestradiol.
J. Kotwica, D. Schams, H. H. D. Meyer and Th. Mittermeier
Summary. In Exp. I oxytocin (60 μg/100 kg/day) was infused into the jugular vein of 3 heifers on Days 14–22, 15–18 and 16–19 of the oestrous cycle respectively. In Exp. II 5 heifers were infused with 12 μg oxytocin/100 kg/day from Day 15 of the oestrous cycle until clear signs of oestrus. Blood samples were taken from the contralateral jugular vein at 2-h intervals from the start of the infusion. The oestrous cycle before and after treatment served as the controls for each animal. Blood samples were taken less frequently during the control cycles. In Exp. III 3 heifers were infused with 12 pg oxytocin/100 kg/day for 50 h before expected oestrus and slaughtered 30–40 min after the end of infusion for determination of oxytocin receptor amounts in the endometrium. Three other heifers slaughtered at the same days of the cycle served as controls.
Peripheral concentrations of oxytocin during infusion ranged between 155 and 641 pg/ml in Exp. I and 18 and 25 pg/ml in Exp. II. In 4 out of 8 heifers of Exps I and II, one high pulse of 15-keto-13,14-dihydro-prostaglandin F-2α (PGFM) appeared soon after the start of oxytocin infusion followed by some irregular pulses. The first PGFM pulse was accompanied by a transient (10–14 h) decrease of blood progesterone concentration. High regular pulses of PGFM in all heifers examined were measured between Days 17 and 19 during spontaneous luteolysis. No change in length of the oestrous cycle or secretion patterns of progesterone, PGFM and LH was observed. The number of oxytocin receptors in endometrium was not affected by oxytocin infusion around the time of oestrus. These results suggest that luteolytic events were not significantly influenced by a constant infusion of oxytocin.
Keywords: oxytocin; infusion; luteolysis; oestrous cycle length