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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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G. W. Randall, J. C. Daniel Jr and B. S. Chilton

Summary. The effect of prolactin on uteroglobin production by immature rabbits was studied with neonatal (1 day old) and juvenile (14 days old) does. The animals were divided into 11 treatment groups for each age category and exposed to a 9-day injection protocol. Each day the animals received a subcutaneous injection of oestradiol-17β and/or ovine prolactin and/or progesterone, or were sham-injected. Juvenile animals, which received 100 μg oestradiol/kg 24 h−1, plus progesterone or plus prolactin and progesterone, produced detectable amounts of uteroglobin in the uterine secretions (0·034 ± 0·010 mg uteroglobin/mg total protein and 0·098 ± 0·031 mg uteroglobin/mg total protein, respectively). None of the animals in the other juvenile treatment groups or any of the neonatal groups produced uteroglobin.

From this survey it was apparent that uteroglobin secretion could be induced by exogenous oestradiol and progesterone in rabbits treated as early as 14 days of age, and that the added supplementation of prolactin enhanced the response to the ovarian steroids. As a result, additional juvenile animals were injected with 100 μg oestradiol ± prolactin + progesterone and the effects of these two treatments were quantitated as follows: uteroglobin mRNA levels by slot-blot hybridization; endometrial surface area by computerized image analysis; and oestrogen, progesterone and prolactin receptors by immunocytochemistry. Prolactin modified the response of the juvenile rabbit uterus to oestradiol + progesterone for all parameters tested.

Keywords: prolactin; uteroglobin; immunocytochemistry; receptors; rabbit

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J. C. Daniel Jr, S. C. Juneja, S. P. Taylor, P. B. Lonergan, P. K. Sullivan and B. S. Chilton

Summary. Ovariectomized rabbits from different breeders were treated at different times of the year with prolactin alone or with progesterone and the production of uteroglobin by the uterus was studied. There were seasonal, strain and dose variables in the uterine response to prolactin and progesterone. Treatment with prolactin (at 1 mg/day) plus progesterone generally induced higher levels of uteroglobin production than did treatment with progesterone alone. The differences were greatest in the winter for Tennessee animals and in the spring for animals from the New Mexico and North Carolina colonies.

Ovariectomy produced a decrease (P < 0·01) in the concentration of cytosolic oestrogen and progesterone receptors, and prolactin treatment restored the concentration to oestrous control values. However, there were no seasonally dependent changes in the concentration of the receptors for any of the treatment groups.

Increased doses of prolactin (2 mg/day) induced high levels of uteroglobin production and new proteins to appear in uterine secretions of long-term ovariectomized rabbits but much lower levels (10–11%) when given to pregnant does. Additional ovulations were also noted plus adverse effects on the embryos.

Keywords: prolactin; rabbit uterus; uteroglobin; progesterone; seasonal variability