Prolonged sensitisation of pituitary glands in vitro to repeated administration of luteinising hormone-releasing hormone: effects of pulse frequency, ovariectomy, estradiol and progesterone.
Anterior pituitary gland fragments were obtained from female Wistar-derived rats on dioestrus or pro-oestrus and perifused in Biogel columns in vitro. They were subjected at the beginning of each of 5 h of perifusion to a volley of 6 1-min pulses of luteinising hormone-releasing hormone (LHRH, 10 nM), given 4 min apart. Luteinising hormone (LH) was measured by radioimmunoassay in sequential 2-min fractions of the perifusate. Pituitary glands removed at 14.00 h on dioestrus showed a characteristic pattern of sensitisation followed by desensitisation to the repeated volleys of LHRH, whereas tissues removed at 10.00 or 14.00 h on pro-oestrus showed no evidence of desensitisation over the 5-hour period, the response to each LHRH volley being greater than the preceding one. Estradiol (E, 3-100 pg/ml) added to the medium from the start of perifusion had no significant effect on the pattern of response from tissues removed on pro-oestrus, but the highest concentration significantly enhanced the response of dioestrus pituitaries to all but the last of the LHRH volleys. Progesterone (P, 1-50 ng/ml) added to the medium produced a dose-related inhibition of the response of pro-oestrous tissues to the LHRH volleys. Groups of animals were ovariectomised (OVX) on dioestrus and used for experiment the next morning. OVX at 10.00 h on dioestrus produced the pattern of response characteristic of dioestrus the next morning, but with much higher levels of LH release, which were unaltered by the addition of E to the medium. OVX at 17.00 h on dioestrus produced an entirely different pattern of response the next day, with high basal and moderate LHRH-induced LH release, and no evidence of changes in sensitivity of the tissue.(ABSTRACT TRUNCATED AT 250 WORDS)
Nicholson
S
S
Aslam
M
M
Gillham
B
B
Jones
M
M
D000818:Animals; D004958:Estradiol / Q000097:blood / Q000494:pharmacology*; D004971:Estrus; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D066298:In Vitro Techniques; D007700:Kinetics; D007986:Luteinizing Hormone / Q000378:metabolism*; D010052:Ovariectomy; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D011374:Progesterone / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains
D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone