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  • Author: M. C. MORRISSETTE x
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R. C. MILLS and M. C. MORRISSETTE

Summary.

Fourteen bovine ovaries of early pregnancy and nineteen of late pregnancy were perfused with citrated bovine blood. During perfusion, the venous blood was collected from each ovary before and after addition of lh and was analysed for progesterone content. Average progesterone synthesis rates were 43·37±1·12 and 4·57±0·99 μg/min before addition of lh, for ovaries of early and late pregnancy respectively, and increased to 7·43±1·98 and 7·72±1·33 μg/min, respectively, after addition of lh. There was no significant difference in the rates of progesterone synthesis between ovaries of early and late pregnancy at the 5% level and their response to lh was highly significant (P<0·01). These data indicate that a decrease in progesterone synthesis during late pregnancy in the bovine is not due to a reduction in the ability of the corpus luteum to respond to gonadotrophins.

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M. C. MORRISSETTE, L. E. McDONALD and R. D. MORRISON

Summary.

A synthetic orally-active progestin, 17α-acetoxyprogesterone (17-ap), given to pregnant rats for the first 13 days of gestation had no apparent effect on ovary, uterus, or implant (the foetus and its membranes) weights, or uterine acid and alkaline phosphatase activity. No follicular cysts were observed in these rats, in contrast to the incidence of follicular cysts observed in pigs in similar experiments. Pituitary luteotropic hormone (probably prolactin) was increased while pituitary luteinizing hormone (lh) was decreased. The theoretical implications of these findings, and the possible role of prolactin in preventing follicular cysts and luteal regression in progestin-treated rats, are discussed.

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G. H. STABENFELDT, E. L. AKINS, L. L. EWING and M. C. MORRISSETTE

Summary.

Progesterone levels were determined in the peripheral plasma of four gilts on each day of the oestrous cycle. An initial rise was observed at Day 3 or 4 of the cycle (oestrus = Day 1) followed by a very rapid increase up to Day 7 or 8 and a slower rate of increase until Day 14 or 15 of a 20-day cycle. The highest levels of progesterone during the luteal phase were about 35 ng/ml plasma and the average concentration during Days 10 to 15 was approximately 27 ng/ml plasma. The decline in progesterone levels after Day 15 was precipitous, a thirty-fold decrease occurring in most cases within 48 hr. Progesterone levels remained low (about 0·5 ng/ml) for about 7 days during the phase of follicle growth and ovulation.

A rather consistent time interval (7 days) was observed between the decline in progesterone concentration and the onset of overt oestrus. The high levels of circulating progesterone in the gilt may suppress follicle development sufficiently during the luteal phase so that approximately 1 week is required between corpus luteum regression and ovulation.

The concentration of plasma progesterone in nine castrated boars was 0·9 ng/ml suggesting an extra-gonadal source of progesterone, possibly adrenal in origin.