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

Mordechai LISCOVITCH*, Nurit BEN‐AROYA, Rina MEIDAN, Yitzhak KOCH

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

17 Scopus citations

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.

Original languageEnglish
Pages (from-to)191-197
Number of pages7
JournalEuropean Journal of Biochemistry
Volume140
Issue number1
DOIs
StatePublished - Apr 1984
Externally publishedYes

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