The physiological responses of anovulatory ewes to the introduction of rams: a review.

Summary

(1) Luteinizing hormone (LH) is secreted as discrete pulses throughout all stages of the reproductive cycle of the ewe, including pre-pubertal, seasonal and lactational anoestrus, and the luteal and follicular phases of the oestrous cycle. Secretion is probably also pulsatile during the preovulatory surge of LH.



(2) The secretion of LH is affected by the ovarian steroids, oestradiol and progesterone, both of which act principally to reduce the frequency of the pulses. During the luteal phase the two steroids act synergistically to exert this effect, and during anoestrus oestradiol acts independently of progesterone. Androstenedione secreted by the ovary apparently has no role in the control of LH secretion.



(3) The amplitude of the pulses may also be affected by the steroids but there are conflicting reports on these effects, some showing that amplitude is lowered by the presence of oestrogen and others showing increases in amplitude in the presence of oestrogen and progesterone.



(4) The secretion of LH pulses is affected by photoperiod, social environment and nutrition. Under the influence of decreasing day-length, oestradiol alone cannot reduce the frequency of pulses and the ewe experiences oestrous cycles. When day-length is increasing, the hypothalamus becomes more responsive to oestradiol which reduces the frequency of the pulses.



(5) A hypothetical pheromone secreted by rams can increase the frequency of the LH pulses in anoestrous ewes and thereby induce ovulation, possibly by inhibiting the negative feedback exerted by oestradiol.



(6) The relationships between nutrition and reproduction are poorly understood, but it seems likely that the effects of nutrition are mediated partly through the hypothalamus and its control of the secretion of LH pulses.



(7) The pulses of LH secreted by the anterior pituitary gland are evoked by pulses of GnRH secreted by the hypothalamus. The location of the centre controlling the GnRH pulses and the neurotransmitter involved are not known.

Factors affecting the secretion of luteinizing hormone in the ewe.

Publisher Summary This chapter discusses a framework for the development of maternal behavior from parturition to weaning considering all the recent studies on mother-young relationships in ewe. Initially, temporary maternal interest in the neonate is elicited through hormonal facilitation. This facilitation is more efficient as the animal has some maternal experience. Maternal interest ensures contact with the newborn lamb, and maternal experience helps the establishment of mother-young contact. From then on the lamb starts to influence the maternal behavior, and sensory information provided by the young become increasingly important. The few hours postpartum during which the ewe can remain maternal in the absence of a young––that is, the sensitive period, probably make up the time when maternal behavior changes from a hormonal regulation to a neurosensory control. After this postpartum period, maternal acceptance of the young seems to become largely independent of the hormonal state of the mother.

Endocrine and Sensory Regulation of Maternal Behavior in the Ewe

SUMMARY The responses of pregnant and nonpregnant ewes on day 13 post-estrus to a dose of prostaglandin (PG)F2a known to be luteolytic in nonpregnant ewes were compared (experi- ment I). Either 270 /ag PGF2~ THAM salt (eight nonmated and 11 mated ewes) or saline (eight nonmated and 10 mated ewes) was injected into the largest follicle on each ovary bearing a corpus luteum. Jugular plasma sam- ples taken just prior to surgery and 4, 8, 12, 16, 20, 24, 28, 32 and 36 hr after injection were analyzed for progesterone, estradiol-1713 and luteinizing hormone (LH) by radioimmuno- assay. Treatment with PGF2a shortened the estrous cycle by 1.5 days in nonmated ewes and mated ewes without embryos (P<.05). Mated ewes with embryos did not return to estrus. The linear regression of progesterone over time varied with treatment (P<.01), pregnancy status (P<.01) and treatment x pregnancy status (P<.09). Progesterone did not reach as low a level (1.3 vs .4 ng/ml; P<.05) in pregnant as in nonmated ewes. Both LH and estradiol- 17/3 increased in treated ewes after progesterone had decreased to approximately 50% of pre- treatment levels; the increase in estradiol was transient in the pregnant ewes. The pattern of LH did not differ with pregnancy status. It is concluded that pregnancy overcame the luteo- lytic effects of PGF2c~ (i.e., had an antiluteo- lytic effect). Experiment II was designed to ascertain whether PGE 2 has antiluteolytic properties. A catheter was inserted into each uterine horn that was ipsilateral to a corpus luteum in nonmated ewes on day 11 postestrus. Intrauter- ine injections of 0, 300, 600 or 900/agof PGE2 were begun on the morning of day 12 and continued every 8 hr until estrus or day 20. Jugular plasma samples were taken just before the first injection and every 24 hr thereafter in all ewes and at .25, .5, 1, 2, 4 and 8 hr from several ewes in each group and were assayed for progesterone. The estrous cycle was lengthened and the decline in progesterone delayed by 2 days by PGE2 (P<.05). Frequent samples on day 12 did not differ in progesterone levels among treatments or over time. Prostaglandin E 2 had antiluteolytic activity in ewes but no in vivo steroidogenic effect was observed. (Key Words: Ewe, Corpus Luteum, PGF2c~, PGE2, Antiluteolytic Factors, Early Preg- nancy.) 1 Division of Animal and Veterinary Science. Sup- ported by NICHD Contract No. 69-2215 and Hatch Project 224 (NE-72). We thank the Upjohn Company and Drs. James Lauderdale and John E. Pike

Antiluteolytic effect of the conceptus and of PGE2 in ewes.

Intra-uterine administration of prostaglandin F,o-tham salt (PGF,a) to ewes on Days 9 or 10 of the estrous cycle was followed by reduced flow of blood to the ovary containing the corpus luteum and reduced levels of progesterone in the systemic circulation. These parameters were highly correlated (P<0.01). In an attempt to separate a direct effect of PG on the luteal cell from the effects on ovarian blood flow, analogs of PGF2o, ICI-79939 and ICI-81008, having 10 times more and 50 times less smooth muscle stimulating activity than PGF2O, respectively, were administered intramuscularly to ewes on Day 10 of the estrous cycle. Levels of progesterone in the systemic circulation and blood flow to the ovary with a corpus luteum decreased to basal levels within 12 h after treatment in both groups of ewes. Ovarian blood flow and systemic progesterone levels were also correlated in ewes receiving ICI-79939 (r = 0.87, P<0.01) and ICI-81008 (r = 0.50, P<0.05) In corpora lutea removed from ewes 0, 6, 12, 24 and 48 h after administration of PGF, o there was a decrease in percentage of the total volume of the corpus luteum occupied by endothelial cells (P<0.001), red blood cells (P<0.01) and lumens of capillaries (P<0.05) with time. There was an increase in cellular debris in the extra-cellular space (P<0.O1) and within capillaries (P<0.05) after injection of PGF2o. Percent volume of the corpus luteum occupied by theca-lutein cells, fibroblasts, eosinophils, connective tissue and white blood cells was not affected by this treatment. Ultrastructurally, cnrpora lutea removed from ewes 6 h after injection of PGF, o were similar to corpora lutea removed from control ewes. By 12 h, a proliferation of coated vesicles, dense bodies and lipid droplets was observed in granulosa-lutein cells and local areas of cytoplasmic degeneration were visible. By 24 h after treatment with PGF2o many of the capillaries which were present contained cellular debris, nucleoli in granulosa-lutein cells were rare and granules within the matrix of the mitochondria were numerous. By 48 h, granulosa-lutein cells were extremely shrunken, contained irregular nuclei with condensed chromatin, abundant lipid droplets and swollen mitochondria. Morphological changes occurring in the theca-lutein cells after administration of PGF2o to ewes were similar to the changes described for granulosa-lutein cells. The data obtained from these experiments indicate that administration of PGF, a to ewes reduced blood flow to the ovary with a corpus luteum and reduced secretion of progesterone. Morphological studies suggested that PGF2o affected the vascular component of the corpus luteum.

Effects of Prostaglandins on the Ovine Corpus Luteum: Blood Flow, Secretion of Progesterone and Morphology

Serial measurements (up to four times per day) of maternal plasma progesterone, corticosteroids, estrone, estradiol-17�, LH, and prolactin have been made in six sheep, during late pregnancy and at parturition (Day 0). The mean progesterone concentration on Day -10 was 15.5 ng/ml. From Day -4 the level began to decrease and by Day 0, the mean progesterone level was 1.0 ng/ml. The mean concentrations of estrone and estradiol-17p on Day -3 (62.4 and 24.0 pg/ml, respectively) began to rise during the 48 hr preceding parturition, reaching peak values of 228.0 and 141.8 pglml, respectively. The mean corticosteroid level (17.3 ng/ml) rose during the 18 hr preceding parturition, reaching a peak of 38.6 ng/ml. Estrone, estradiol-17�, and corticosteroids returned to low levels within 12 hr after parturition. LH levels remained relatively coastant (2.0-6.0 ng/ml) from -36 h to +30 h but prolactin levels rose sharply from about Day -2. Possible explanations for the absence of an increase in LH secretion, in response to the preparturient rise in estrogens, are discussed.

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Changes in the Levels of Progesterone, Corticosteroids, Estrone, Estradiol-17 β, Luteinizing Hormone, and Prolactin in the Peripheral Plasma of the Ewe During Late Pregnancy and at Parturition

THE EFFECT OF PROSTAGLANDIN F2α ON PROGESTERONE, OESTRADIOL AND LUTEINIZING HORMONE SECRETION IN SHEEP WITH OVARIAN TRANSPLANTS

A synthetic decapeptide (Gn-RH) structurally identical to ‘ovine LH-releasing hormone’ was given by intra-carotid infusions (0, 0.5 and 1.5 µ g/h for 3 h) to two groups of ewes late

Effect of progesterone on the release of luteinizing hormone induced by a synthetic gonadotrophin-releasing factor in the ewe.

The function of the metrial gland of the rat, and particularly of its characteristic population of granulated cells, remains unknown. However, several lines of evidence suggest that the granulated cells may derive from lymphocytes, and play a role in the immunology of pregnancy. In this study, antigen expression by granulated and other cell populations from the metrial glands of rats at Days 13 and 14 of pregnancy was studied by an indirect immunoperoxidase method. Acetone-fixed frozen sections, and cytocentrifuge preparations of collagenase-dispersed metrial gland tissue in which numbers of granulated cells had been increased by density-gradient centrifugation, were used. The primary antibodies used recognised, inter alia, B lymphocytes (MRC OX-3, MRC OX-6, MRC OX-12), T lymphocytes (MRC OX-8, W3/25, MRC OX-19), neutrophils (MRC OX-42) and cells of the monocyte/macrophage series (MRC OX-3, MRC OX-6, MRC OX-42, MRC OX43). The majority of the granulated cells, including smaller, “immature” forms, were unlabelled by any of these antibodies. Some lymphocytes, and varying numbers of larger, non-granulated cells, were labelled by OX-6, OX-12, W3/ 25, OX-42 and OX-43. In addition to lymphocytes, labelled cells included neutrophils (OX-42), endothelial cells (OX-43), and probably some macrophages (OX-6, OX-43). OX-12, which recognises the kappa chain of rat IgG, labelled some large cells which may have been stromal cells. These findings do not support the concept that the granulated cells are derived from lymphocytes.

Expression of leucocyte antigens by cells from the metrial gland of the pregnant rat

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Mildred E. Cerini

Papers

Changes in the Levels of Progesterone, Corticosteroids, Estrone, Estradiol-17 β, Luteinizing Hormone, and Prolactin in the Peripheral Plasma of the Ewe During Late Pregnancy and at Parturition

THE EFFECT OF PROSTAGLANDIN F2α ON PROGESTERONE, OESTRADIOL AND LUTEINIZING HORMONE SECRETION IN SHEEP WITH OVARIAN TRANSPLANTS

Effect of progesterone on the release of luteinizing hormone induced by a synthetic gonadotrophin-releasing factor in the ewe.

Expression of leucocyte antigens by cells from the metrial gland of the pregnant rat

Luteal Function Following the Infusion of Prostaglandin F2α into the Uterine Vein of the Ewe