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A. Krishna, P. F. Terranova, R. L. Matteri, and H. Papkoff

Summary. Constant infusion of LH (400 μg NIH-S24) through an osmotic minipump inserted on Day 1 (oestrus) of the cycle in the hamster resulted in spontaneous superovulation (≃ 29 ova) at the next expected oestrus, increased blood flow (P<0·001) to the ovary on Day 3, and slight depletion (0·1 >P>0·05) of histamine in the ovary. Treatment with antihistamine (alpha-fluoromethylhistidine, an irreversible inhibitor of histidine decarboxylase, or cimetidine, an H2 blocker) by injections or by infusion using separate osmotic minipumps significantly (P<0·01) reduced the number of ova shed in the LH-treated hamsters. Infusion of LH with alpha-fluoromethylhistidine in the same osmotic minipump reduced the bioactivity of the LH. Infusion of antihistamine alone did not alter the normal number of ova shed. The results suggest that the LH-induced superovulation involves stimulation of histamine release; the histamine then may increase ovarian blood flow thus allowing more gonadotrophins to reach the ovary.

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J. D. Brannian, F. Griffin, H. Papkoff, and P. F. Terranova

Summary. Serum samples were collected from 3 mature female African elephants once each week for 15–18 months. Circulating concentrations of progesterone, oestradiol and LH were determined by radioimmunoassay (RIA). The LH RIA was validated by demonstrating parallel cross-reaction with partly purified elephant LH pituitary fractions. Changing serum progesterone concentrations indicated an oestrous cycle length of 13·3 ± 1·3 weeks (n = 11). The presumed luteal phase, characterized by elevated serum progesterone values, was 9·1 ± 1·1 weeks (n = 11). Two abbreviated phases of progesterone in serum lasting 2–3 weeks were observed in 2 elephants, indicating short luteal phases. Oestradiol concentrations in serum were variable, with no clear pattern of secretion. More frequent blood samples were collected during periovulatory periods and 9 distinct LH peaks were detected; all were followed by rises in serum progesterone concentrations. Periovulatory changes in progesterone and LH in sera correlated with external signs of oestrus and mating behaviour.

Keywords: elephant; Loxodonta; oestrous cycle; progesterone; LH

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V. M. Shille, Coralie Munrot, Susan Walker Farmer, H. Papkoff, and G. H. Stabenfeld

Summary. LH release leading to ovulation was induced in 17 of 29 oestrous periods. The time of ovulation after coitus was determined by histological examination or by observation at laparotomy of ovaries in situ. Histological methods revealed that ovulation was complete in most follicles (9 of 13) at 32 h post coitum and in all follicles that were involved in the ovulatory process by 36 h. When laparotomy was used, no signs of preovulatory change were noted at the first observation time, 22 h post coitum, but in 4 cycles in which the entire process of ovulation was observed, the ovulatory process occurred between 23 and 28 h (3 follicles), 23 and 27 h (2 follicles), 25 and 28 h (3 follicles), and 25 and 29 h (3 follicles)post coitum. The first ovulatory process noted was complete at 25 h post coitum.

In cats, LH release continued over a 16-h period before returning to baseline (long surge), values being 616 ± 180 ng/ml at ½ h and 941 ± 154 ng/ml at 2 h post coitum. In 6 cats the LH release pattern was limited to a 4-h period (short surge), values being 537 ± 218 ng/ml at ½ h and 353 ± 245 ng/ml plasma at 2 h and basal (49 ± 18 ng/ml) by 4 h post coitum. Decreased secretion of oestrogen by follicles in animals undergoing ovulation was first observed at 16 h post coitum.

It is concluded that coitus induces LH release within minutes in the cat and that ovulation begins about 24 h later and finishes by about 32 h post coitum. Only one coital input can cause LH release for as long as 16–20 h although shorter periods of LH release (4 h or less) can result in ovulation.

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D. J. Tortonese, P. E. Lewis, H. Papkoff, and E. K. Inskeep

Summary. Prepubertal crossbred beef heifers were injected (i.v.) with 50 μg bovine LH every 2 h for 48 h (first injection at 0 h). At 28 h, number and diameter of ovarian follicles were determined by ultrasonic scanning, and unilateral removal of either the ovary bearing the largest follicle (Group UL, N = 5) or the opposite ovary (Group UO, N = 4) was performed; control animals remained intact (Group I, N = 5). Blood samples were taken every 2 h (starting at 0 h) for a 60-h period to assess concentrations of gonadotrophins and oestradiol. Preovulatory-like surges of LH occurred in 0/5, 4/4 and 5/5 heifers for Groups UL, UO and I respectively; the time of the LH surge did not differ between animals in Groups I and UO (mean = 40 h). FSH in Group UL heifers rose to a plateau immediately after unilateral ovariectomy; this pattern was not observed in the other two groups (P < 0·01). The area under the curve for FSH was significantly different (P < 0·05) among groups after 28 h. Preovulatory-like surges of FSH occurred coincidently with those of LH, except for one Group I heifer. An increase in the concentrations of oestradiol between 0 and 28 h was detected in all animals. Profiles of oestradiol during this period did not differ between heifers that had an LH surge (Groups UO and I) and those that did not (Group UL). After 28 h, concentrations of oestradiol declined to basal levels in Group UL heifers, but in the other two groups it was not possible to characterize, by linear, quadratic or cubic regression, any particular pattern of oestradiol before the LH surge. Ovulation, as determined by rectal palpation and concentrations of progesterone, occurred in 0/5, 4/4 and 4/5 animals for Groups UL, UO and I, respectively. All induced luteal phases were of short duration (<9 days). It is concluded that: (1) repeated injections of LH in the prepubertal heifer are able to induce surges of gonadotrophins and formation of a corpus luteum, (2) the ovary containing the largest follicle is required to mediate the stimulatory effect leading to the LH and FSH surges, and (3) the opposite ovary plays no important role in this mechanism.

Keywords: LH; FSH; oestradiol; dominant follicle; prepubertal heifers