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J. C. DANIEL Jr

A gradual increase in blastokinin (BKN) concentration in the uterus of the rabbit has been noted between Days 2 to 5 (or 6) of pregnancy (Krishnan & Daniel, 1967) and pseudopregnancy (Johnson, 1972) or after progesterone administration (Arthur & Daniel, 1972). It is possible that all of the BKN-producing tissue (presumed to be the endometrim) could initiate BKN production at about the same time and accelerate it thereafter to reach a maximum level some 2 to 3 days later. A second possibility is that there is one local region that begins to secrete BKN, and this is followed by progressive expansion of the secretory areas; for example, the secreting activity might begin at the tubal end of the uterus early on Day 3 post coitum and then progress caudally

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J. C. Daniel Jr

Two recent reports of plasma progesterone levels during early pregnancy in the ferret show significant differences during and immediately before implantation. Heap & Hammond (1974) found peak progesterone levels on Day 12 while Blatchley & Donovan (1976) recorded a maximal level on Day 14 that was approximately half that reported by Heap & Hammond (1974) for the same day using the same technique (radioimmunoassay). Heap & Hammond also measured progesterone by fluorometric and competitive protein-binding assays and found levels 2–3 times higher than did Blatchley & Donovan. In this paper I report an attempt to resolve this difference.

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J. C. DANIEL Jr

From morphological, physiological and biochemical observations, Shelesnyak, Kraicer & Zeilmaker (1963) demonstrated the existence of an `oestrogen surge' in the rat occurring on Day 3 of either pregnancy or pseudopregnancy (spermatozoa in the vaginal smear on Day 0). This observation was confirmed by Shaikh & Abraham (1969) with radioimmunoassay for oestradiol concentration in ovarian venous blood plasma. The oestrogen surge coincides with the period of blastocyst development immediately preceding implantation. Furthermore, an artificial surge produced by exogenous oestradiol-17β in rodents ovariectomized before Day 3 terminates a state of facultative delayed implantation by reactivation of blastocysts in diapause (Cochrane & Meyer, 1957).

McLaren (1972) has suggested that ".....the necessity for an oestrogenic intervention at the time of implantation,....., may be characteristic of those species where the embryo undergoes delayed implantation". We were interested in determining whether a representative of a group having obligatory delayed implantation might also have an oestrogen surge

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MARILYN J. VEOMETT and J. C. DANIEL Jr

Summary.

The activity of 20α-hydroxysteroid dehydrogenase (20α-HSD) was assayed in the ovaries of rats after accelerated lactation to determine its relationship to the decrease in progesterone secretion that occurs. When rats were subjected to accelerated lactation on Day 9 of pregnancy, activity of the enzyme was only slightly increased by Day 10, but had risen to twice the control level by Day 11, and three times the control level by Day 12. Administration of LH or progesterone prevented the increase in enzyme activity. Progesterone concentration had decreased considerably before the time at which any significant increase in 20α-HSD activity was detected. These findings are discussed in relation to the role of 20α-HSD in regulating progesterone levels in the rat.

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MARILYN J. VEOMETT and J. C. DANIEL Jr

Summary.

Pregnancy is terminated in rats that have mated at the post-partum oestrus if they are allowed to suckle a large litter after implantation. For consistent termination, the number of sucking young must be at least nine, the accelerated lactation must be begun before Day 10 of pregnancy, and must be continued for at least 2 days.

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MARILYN J. VEOMETT and J. C. DANIEL Jr

The gestation period in rats that have bred during a post-partum oestrus is known to be lengthened if the female is suckling a moderately large litter. Presumably, this lengthening is due to a prolongation of the progestational period and the embryos may remain dormant in the blastocyst stage for up to 14 days (Weichert, 1940; Psychoyos, 1970).

We wanted to determine whether heavy lactation might also induce dormancy in postimplantation embryos or if other effects might take precedence, for example, if the mother would continue to suckle the large litter or if the pregnancy would be terminated.

Holtzman strain rats were used throughout the experiment. Pregnant females were caged with experienced males at least 8 days before parturition. Post-partum mating was checked by vaginal smears

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MARILYN J. VEOMETT and J. C. DANIEL Jr

Summary.

The relationship was investigated of the hormones associated with pregnancy and lactation and the termination of pregnancy that occurs when rats mated at the post-partum oestrus are allowed to suckle a large litter after implantation. The primary cause for pregnancy termination was found to be an insufficient level of progesterone with the possible need for a primary or synergistic dose of oestrogen. The progesterone deficiency was not due to the high levels of prolactin present in nursing rats, since pregnancy termination could not be produced by prolactin administration in the absence of accelerated lactation, and could not be prevented by blocking prolactin secretion after accelerated lactation. Administration of LH to rats after accelerated lactation did prevent termination of pregnancy.

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J. C. Daniel Jr and J. W. Crowder

The glycoprotein blastokinin was originally thought to be unique to the rabbit uterus (Krishnan & Daniel, 1967) but a similar molecule has been reported to be present in the oviduct (Kay & Feigelson, 1972). Beier & Kühnel (1974) reported its presence in semen and Noske & Feigelson (1976) have found a blastokinin-like antigen in other parts of the female tract, the male tract, and parts of the digestive and respiratory tracts; observations that were confirmed in part by Kirchner & Schroer (1976) and Daniel & Milazzo (1976). Because the amount of blastokinin in the uterus varies with the endocrinological state of the doe, being especially pronounced before implantation, we questioned if the blastokinin-like antigen of other tissues also varies in the same way. Here we report our studies of the blastokinin content of lung tissue throughout early pregnancy with additional comparison of samples taken later in pregnancy and from ovariectomized does, some treated with progesterone, and from males.

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B. S. Chilton and J. C. Daniel Jr

Summary. The direct effect of growth hormone (GH) on the uterine response to progesterone was tested by using ovariectomized rabbits (at least 12 weeks) treated with GH; GH + progesterone; or progesterone alone. These results were compared with the effect of prolactin or prolactin + progesterone on the uterus. Prolactin treatment produced an increase (P < 0·01) in the endometrial surface area and restored cytosolic oestrogen and progesterone receptor concentrations to oestrous control values. The sequential treatment of does with prolactin + progesterone stimulated uteroglobin production to a concentration equal to that found in intact rabbits on Day 5 of pregnancy. In contrast, GH treatment had no effect on endometrial surface area, produced an increase in the concentration of cytosolic oestrogen receptor but did not produce an increase in the concentration of progesterone receptor. The sequential treatment of does with GH + progesterone failed to stimulate uteroglobin secretion above control (progesterone alone) values. It is concluded that the action of prolactin in the rabbit uterus is not generally somatogenic; rather, prolactin increases the concentration of progesterone receptor and thereby enhances the uterine response to progesterone.

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I. G. NOSKE and J. C. DANIEL Jr

Summary.

The total protein concentration was measured in flushings from the hamster reproductive tract during the first 6 days of pregnancy. Protein concentrations reached their highest level in uterine flushings on Day 3 p.c., shortly before the time of implantation.

The protein concentrations in the oviducal fluid fluctuated more than in the uterine fluid, possibly because the oviducal flushings were more prone to serum contamination.

Electrophoretic analysis of uterine and oviducal fluid proteins revealed qualitative and quantitative changes. In both cases, the patterns increasingly resembled those of serum proteins during development. The appearance of a new protein band on Day 3 p.c. was particularly noted. Also of interest was the appearance of a band on Day 4 p.c. in oviducal fluid and the disappearance of one band on Day 5 p.c.