Peripheral Plasma Levels of Luteinizing Hormone-Releasing Hormone-Like Immuno-reactivity and Luteinizing Hormone in Anestrous and Ovariectomized Sheep

Summary

Low levels of endogenous LHRH-like immunoreactivity (IR) were consistently detected in methanolic extracts of plasma samples from anestrous and ovariectomized sheep. Mean concentrations were similar in magnitude in the intact and castrate ewes (7.7±0.7 and 6.1±0.8 pg/ml, respectively) but revealed greater within animal fluctuations in the ovariectomized sheep (CVs: anestrous ewes = 20±3 %; ovariectomized ewes = 45±10 %). Patterns of plasma LHRH-like IR and LH levels were not obviously related. Differences in levels of LHRH-like IR did exist between ewes and in the ovariectomized sheep the levels were positively correlated (r = .83, P < ,05) with the pituitary LH response to synthetic LHRH injection (0.25 μg). Large plasma volumes (250ml) were extracted using chloroform, methanol and acetic acid and then chromatographed using Sephadex LH-20. Plasma LHRH-like IR could be concentrated and was found to have a column elution volume coincident with that of synthetic LHRH. These data indicate that there is a substance in ovine plasma which is close in size, solubility and IR to sLHRH. It does not reflect plasma LH levels in either magnitude or pattern but does exhibit a coincident increase in variation with plasma LH levels following ovariectomy and appears to be associated with the pituitary responsiveness.

Key-Words:

Plasma LHRH-Like Immunoreactivity - LH - Sheep