The effects of stimulating the immune system with lipopolysaccharide (LPS) or suppressing the immune system with cyclosporin (CS) on reproductive functions in the female rat were investigated. Animals were either treated acutely with LPS (2 mg kg⁻¹) or cyclosporin (20 mg kg⁻¹) on dioestrus day 1 and 2 or treated chronically over a period of 6 days (on alternate days with LPS, daily with CS). Chronic LPS treatment induced a state of constant dioestrus and decreased circulating concentrations of progesterone and oestradiol. Chronic CS treatment induced some irregularity in the 4-day vaginal smear pattern in a minority of animals and, while it had no effect on circulating concentrations of progesterone, oestradiol concentrations were suppressed compared with those measured in pro-oestrous animals. LH responses to GnRH were reduced in both perifused pituitary fragments and cultured pituitary cells obtained from animals pretreated with either LPS or CS. In contrast, a low dose of LPS (20 μg kg⁻¹) given over 6 days did not disrupt ovarian cycles and reduced, but did not abolish, the second phase primed LH response. Neither drug had a direct effect on the pituitary LH responses to GnRH, except that pituitary cells exposed to high doses of CS for periods greater than 48 h did show attenuated LH responses to GnRH. This finding was not paralleled with high doses of LPS. The differential count of ovarian follicles from histological studies showed that LPS treatment was associated with significantly fewer large preovulatory follicles, whereas animals treated with CS showed a similar distribution of follicular volumes compared with controls. Results suggest that the hypothalamic–pituitary control of ovarian function is impaired by both LPS and CS treatment, and LPS appears to have an additional effect in suppressing ovarian functions, possibly via an inhibitory action on steroidogenesis.

A comparison was made between the properties of LH derived from female rat pituitary glands and plasma. Samples were collected from adult intact rats 5 h before or at the time of the pro-oestrous preovulatory LH surge; 27-day-old rats untreated or given 5 iu pregnant mares' serum gonadotrophin (PMSG) s.c. on day 25, which induced LH release 54 h later and adult ovariectomized rats untreated or primed with either 5 μg oestradiol benzoate s.c. or 5 μg oestadiol benzoate followed 48 h later by 0.5 mg progesterone s.c., which induced LH release 4–6 h later. All pituitary LH samples were totally bound to an anionic ion-exchange resin (DE52), while only a small proportion of the plasma LH was bound. Only 0–10% plasma LH obtained from intact, ovariectomized (with and without steroids) and untreated immature rats was bound, while a greater proportion of bound LH (36%) was noted in rats treated with PMSG. Gel filtration indicated only slight differences between pituitary and plasma LH, the former eluting marginally earlier than whole plasma and the unbound and bound plasma forms derived after separation by DE52 resin. Affinity chromatography (Concanavalin A and Glycine maximus) showed that LH from both sources possesses high mannose oligosaccharides and that plasma LH does not bear terminal N-acetyl galactosamine residues, although 20% of the pituitary form does. Plasma obtained from pro-oestrous rats had greater bioactivity than had pituitary LH in stimulating testosterone from Leydig cells and progesterone from granulosa cells in vitro, and inducing ovulation in immature rats in vivo. Leydig cell bioassays for LH in fractions obtained from ion-exchange separation indicate that steroidogenic activity of unbound plasma LH is greater than bound pituitary LH when they were collected at times of enhanced release. When release was inhibited (oestrogen-primed ovariectomized rats or immature rats), the steroidogenic activity of plasma and pituitary LH were similar and an acidic steroidogenic component was present in the plasma that was not recognized immunogenically as LH. In summary, pituitary LH undergoes a conversion on release into the plasma that involves a change in binding characteristics on an ion-exchange resin. In conditions when LH release is enhanced there is an increase in bioactivity of plasma LH owing to modification either by steroids or some other plasma factor(s) that perhaps influence the structure of LH directly or by steroids acting indirectly to alter GnRH release, which then modifies LH structure. These structural changes are minor and probably involve alterations in the glycosyl attachments.