LHRH receptor, LH and FSH concentrations in anterior pituitaries of cycling, noncycling and early pregnant heifers

In domestic animals limited data are available concerning levels of pituitary luteinizing hormone-releasing hormone (LHRH) receptors during various physiological states. The objectives of this study were to quantify anterior pituitary gonadotropin and LHRH receptor concentrations in cycling, noncycling and early pregnant beef heifers. To accomplish these objectives, five heifers each were slaughtered, after synchronization with prostaglandin F2 alpha (PGF2 alpha), on d 0 (estrus), 7 and 14 of the estrous cycle and d 40 of pregnancy. Four heifers determined to be noncycling were also slaughtered. Pituitaries were collected and analyzed for LHRH receptor and gonadotropin concentrations. Pituitary luteinizing hormone (LH) concentrations were low on d 0 (1.4 +/- .2 micrograms/mg pituitary, mean +/- SE) and remained low on d 7 (1.4 +/- .1 micrograms/mg pituitary) before increasing (P less than .01) on d 14 (2.6 +/- .5 micrograms/mg pituitary). Luteinizing hormone concentrations, compared with d 0, were also elevated (P less than .01) in noncycling (NC; 2.6 +/- .2 micrograms/mg pituitary) animals and in 40-d pregnant (PG; 2.5 +/- .2 micrograms/mg pituitary) heifers. Pituitary follicle stimulating hormone (FSH) concentrations, though similar (P greater than .05) for all groups, paralleled changes in LH concentration. Pituitary LHRH receptor binding affinity did not differ (P greater than .05) among groups, with an overall Kd = .64 +/- .02 X 10(-9) M. Luteinizing hormone-releasing hormone receptor concentrations were highest on d 0 (1.09 +/- .12 fmol/mg pituitary) and fell (P less than .01) to low levels on d 7 (.75 +/- .11 fmol/mg pituitary).