Plasma relaxin immunoactivity during the oestrous cycle of the ewe.

Plasma relaxin immunoactivity was measured every 2 hr during 4-day periods in a series of sheep to cover the 17-day period of the ovine oestrous cycle. The immunoactivity fluctuated considerably throughout eacn 4-day period, and a large betwee-animal variation was found. A marked episodic release, occurring at approximately 12.00 and 24.00 hours, was identified and shown to occur more regularly either at certain times of the cycle or in certain animals. Relaxin immunoactivity was high throughout the late pro-oestrous phase of the cycle (Days 15 and 16), and at 24 hr after the onset of the LH peak, conincidnet with the approximate time when ovulation occurs. Bursts of relaxin activity were found on Days 8 to 9 in one ewe, and Days 10 and 11 and 13 to 14 in another. There was no significant correlation between prolactin levels and relaxin immunoactivity in one ewe studied throughout the oestrous period.     

Secretion of LH, FSH and oestradiol-17 beta during the follicular phase of the oestrous cycle in the ewe

Plasma concentrations of LH, FSH and oestradiol-17 beta were measured in blood samples taken at 15 min intervals for 48 h during the follicular phase of four Merino ewes. The amplitude of pulses of LH and the mean concentration of LH were higher at the beginning of the follicular phase, 36-24 h before the preovulatory surge of LH (amplitude 2.4 ng ml-1, mean concentration 3.9 ng ml-1), than at the end, 24-0 h before the preovulatory surge (amplitude 1.2 +/- 0.1 ng ml-1; mean concentration 1.4 +/- 0.1 ng ml-1). There was no change in the inter-pulse interval during this time (mean 74 +/- 5 min). Over the same period, oestradiol levels increased from 7-8 pg ml-1 to a peak of 10-15 pg ml-1. Mean FSH concentrations declined (36-24 h: 3.6 ng ml-1 vs 24-0 h: 1.8 +/- 0.3 ng ml-1) before rising at the time of the preovulatory surge of LH and again 24 h later. It was concluded that the biphasic response of LH to oestrogen that is seen in ovariectomized ewes may also operate during the follicular phase of the oestrous cycle in entire ewes.     

Glucose uptake and lactate production by the autotransplanted ovary of the ewe during the luteal and follicular phases of the oestrous cycle

Two experiments were carried out on ewes with ovarian autotransplants to estimate the ovarian uptake of glucose and production of lactate. The first was carried out in the luteal phase of the oestrous cycle. Samples of carotid arterial, ovarian venous and jugular venous blood were collected simultaneously for glucose analysis. The arterial concentration of glucose (58.0 ± 5.0 mg/dL; Mean ± SEM) was significantly higher than the ovarian venous concentration (42.3 ± 2.4 mg/dL; P < 0.001). Next, a second more complete experiment was carried out in the luteal and follicular phases of the oestrous cycle. The oestrous cycle was synchronised and samples of carotid arterial, ovarian venous and jugular venous blood were collected simultaneously for glucose and lactate analysis. There were significant positive arterio-venous differences in the concentration of glucose in the luteal (5.6 ± 1.2 mg/dL, mean ± SEM; P = 0.001), early (3.1 ± 0.82 mg/d; P = 0.003) and late follicular (6.4 ± 1.3 mg/dL; P = 0.001) phases of the oestrous cycle. There was a significant negative arterio-ovarian venous difference in the concentration of lactate in only the luteal phase (-2.2 ± 0.96 mg/dL; P = 0.043).The results show significant removal of glucose from the arterial circulation during its passage through the ovary in the luteal, early follicular and late follicular phases of the oestrous cycle. Furthermore, there was lactate production in the luteal phase but not in the follicular phase suggesting that in the luteal phase of the oestrous cycle, ovarian metabolism can be anaerobic.     

Immunoglobulins in the mouse uterus during the oestrous cycle

The distribution of IgA, IgG and IgM was studied by an immunoperoxidase technique on sections of mouse uteri at each stage of the oestrous cycle. Staining for IgG and IgA was highest at pro-oestrus, declined at oestrus and was very low during the other stages. At pro-oestrus IgG was found throughout the stroma, in the uterine lumen, and in 10% of glandular lumina; very few IgG-containing plasma cells were present. At pro-oestrus, IgA was found in the uterine lumen, and in most of the uterine glands, both in the lumen and in the epithelium; little IgA was present in the stroma. IgA-plasma cells were detected at each stage of the cycle and were particularly numerous at pro-oestrus and oestrus. These results suggest that IgA is secreted locally from plasma cells into the uterine gland through the glandular epithelium, but that IgG enters the stroma from the local capillaries. The obvious increase in IgG and IgA secretion at pro-oestrus, when plasma oestradiol levels are highest, supports the hypothesis that, during the oestrous cycle, the humoral immune response is regulated in the uterus by ovarian hormones.     

Experiments on egg transfer in the cow and ewe: dependence of conception rate on the transfer procedure and stage of the oestrous cycle.

The effects on embryo survival of procedures used in transferring eggs non-surgically were investigated in three experiments in ewes and heifers. In Exp. 1, two techniques for introducing eggs into the uterus through the cervix in heifers were compared; namely (i) deposition of the eggs high into the uterine horn or (ii) into the body of the uterus. Both methods were followed by inflation of the uterus with carbon dioxide. Out of a total of 34 heifers, only one became pregnant by the use of Method (i). Non-surgical egg tansfers early (Days 3 to 5) or later (Days 6 to 9) in the oestrous cycles of heifers were carried out in Exp. 2. Three transfer procedures were compared: (i) pipette transfer of an egg into the body of the uterus through the cervix (control), (ii) the control procedure performed under Fluothane anaesthesia, or (iii) followed by inflation of the uterus with carbon dioxide. Wide transfers carried out early in the cycle, pregnancies resulted in 1/10, 0/10 and 1/10 of the heifers in the control, carbon dioxide and Fluothane groups, respectively. With late transfers, 7/20, 1/10 and 8/20 heifers became pregnant in the respective treatment groups. This trend for pregnancy rate to be improved when late transfers were done in the control and Fluothane groups was significant only at the 10% level of probability when both groups were pooled. It was tentatively concluded, however, that non-surgical transfers of fertilized eggs to heifers may be best done during mid-cycle, after Day 6. Fluothane anaesthesia did not improve conception rate. Inflation of the uterus with carbon dioxide appeared to be deleterious when used at the mid-cycle stage in heifers. In Exp. 3, it was found that inflation of the ewe's uterus with carbon dioxide or nitrogen following the surgical thansfer of an egg did not affect the incidence of pregnancy. The introduction of 50 mul liquid Fluothane into the lumen of the uterus was embryotoxic.     

Scent-marking and the oestrous cycle of the female rat

Oestrous rats scent-mark conspicuous objects and the ground significantly more than they do when they are in dioestrus. The scent-marking behaviour leaves a conspicuous trail of urine and sebaceous secretion. It is suggested that the increased marking at oestrus is functional in attracting males, although the causal factors for it are at present unknown.