title: A differential effect of trypsin on pituitary gonadotropin-releasing hormone receptors from intact and ovariectomized rats. Evidence for the existence of two distinct receptor populations.
abstract: The present report demonstrates that pituitary receptors for gonadotropin-releasing hormone generated following ovariectomy are susceptible to the action of trypsin while those present in intact metestrous females are not. The action of trypsin of gonadotropin-releasing hormone receptors in pituitary cells derived from ovariectomized rats was dependent on time and dose. Trypsin exerted a maximal effect of 40-50% reduction without causing full abolition of the binding activity, indicating that two populations of gonadotropin-releasing hormone receptors can be differentiated in pituitaries derived from ovariectomized rats: one which is sensitive to limited proteolysis by trypsin and another which is resistant to it. Scatchard analysis of gonadotropin-releasing hormone antagonist binding to homogenate of trypsin-treated hemipituitaries derived from ovariectomized rats, revealed that trypsin reduced receptor density while slightly increasing binding affinity. The in vitro responsiveness of hemipituitaries from ovariectomized rats to gonadotropin-releasing hormone and to K+-induced depolarization was reduced following trypsin treatment, while that of hemipituitaries derived from metestrous females was not affected or increased. Trypsin reduced the maximal response level by 30-50% but did not modify the median effective dose of gonadotropin-releasing hormone (1 nM). The reduced gonadotropin-releasing hormone receptor density and the lower responsiveness caused by trypsin in pituitary tissue from ovariectomized rats are not due to a selective loss of gonadotrophs, as trypsin treatment did not affect the lutropin content of the glands. These findings indicate that two populations of gonadotropin-releasing hormone receptors can be distinguished on the basis of their susceptibility or resistance to limited proteolysis by trypsin and suggest that these two gonadotropin-releasing hormone receptor populations are reciprocally affected by ovariectomy.
mesh_terms: D000818:Animals; D002369:Castration; D005260:Female; D010053:Ovary / Q000502:physiology*; D010902:Pituitary Gland / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism*; D011966:Receptors, LHRH; D014357:Trypsin / Q000494:pharmacology*
chemical_list: D011956:Receptors, Cell Surface; D011966:Receptors, LHRH; D014357:Trypsin