Specificity of short-loop feedback of luteinizing hormone in the rabbit.

The specificity of the gonadotropin short-loop feedback mechanism was investigated in castrated rabbits by blood sampling from an indwelling jugular venous catheter for follicle-stimulating hormone (FSH) after the intravenous administration of purified human luteinizing hormone (hLH). Although we have previously shown that such hLH administration results in a decrease of rabbit LH, no decrease in rabbit FSH was seen in these experiments. This specificity of LH feedback is compatible with the site of feedback being at the (1) pituitary level or (2) at the hypothalamic level provided two separate LH and FSH releasing factors exist.