title: Release of luteinizing hormone and follicle-stimulating hormone from pituitaries of lactating rats by gonadotropin-releasing hormone and high potassium concentration.
abstract: Anterior pituitaries (APs) from lactating rats were studied in vitro to determine the mechanisms by which LH release, but not FSH release, is suppressed. Hemipituitaries were exposed for 4 h to GnRH (20 nM) or elevated potassium (K+; 57 mM) according to two different regimens: 6 min/h (pulsatile) or 60 min/h (continuous). Pulsatile K+ exposure stimulated similar amounts of LH release by APs from diestrous females and lactating females on day 5 or 10 who were nursing two or eight pups. Pulsatile GnRH stimulation resulted in significantly greater amounts of LH release from all groups than was observed after pulsatile K+, except by APs from females nursing eight pups. In this group, GnRH was no more effective than K+ in stimulating LH release by APs from day 5 of lactation, but was slightly but significantly more effective on APs from day 10 of lactation. The degree of suppression of GnRH-stimulated LH release was directly correlated with the intensity of the suckling stimulus, and removal of the eight-pup suckling stimulus for 48 h completely restored the LH response to GnRH to the response observed by APs from females on diestrous day 2. Exposure of the APs continuously to either K+ or GnRH produced results that were similar to those observed after the pulsatile regimen, except that the total amount of LH released during the 4-h incubation was greater. However, APs from females suckling eight pups still released significantly less LH in response to GnRH than did APs from females suckling two pups or diestrous females. FSH secretion by the APs was similar in response to either pulsatile K+ or GnRH stimulation and was not suppressed by suckling of a large litter. The total amount of FSH released by pituitaries from lactating and cycling animals did not differ significantly, except that by APs females deprived of their eight-pup litters for 48 h, in which case pulsatile GnRH stimulated a greater amount of FSH release. However, the pattern of FSH release varied, in that pulsatile GnRH stimulation of diestrous pituitaries showed a priming response, whereas no priming response was evident during lactation. Exposure of APs to elevated K+ continuously produced little more FSH release than exposure to pulsatile K+ stimulation. However, continuous stimulation by GnRH generally released more FSH than did K+. FSH responses to GnRH by pituitaries from lactating females were similar or greater than the FSH responses by pituitaries from diestrous females.(ABSTRACT TRUNCATED AT 400 WORDS)
authors.forename: M S
authors.initials: MS
authors.lastname: Smith
mesh_terms: D000818:Animals; D005260:Female; D005640:Follicle Stimulating Hormone / Q000378:metabolism*; D066298:In Vitro Techniques; D007774:Lactation; D007986:Luteinizing Hormone / Q000378:metabolism*; D010903:Pituitary Gland, Anterior / Q000378:metabolism*; D010906:Pituitary Hormone-Releasing Hormones / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology*; D011247:Pregnancy; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000032:analysis; D011966:Receptors, LHRH
chemical_list: D010906:Pituitary Hormone-Releasing Hormones; D011956:Receptors, Cell Surface; D011966:Receptors, LHRH; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D011188:Potassium