Changes in serum luteinizing hormone following intraventricular and intravenous injections of luteinizing hormone-releasing hormone in the rat

A comparison was made of the effects of administer- ing luteinizing hormone-releasing hormone (LH-RH) by the intra- venous (i.v.) vs. intraventricular routes to ovariectomized estrogen- primed rats. I.H-RH was effective by cither route in causing an increase in serum LH as measured by radioimmunoassay, but i.v. injection induced the greater LH discharge. The time courses of the LH responses were identical by the two approaches. A cross- transfusion technique failed to demonstrate the uptake of intra- ventricularly injected LH-RH into the general circulation. These results support the feasibility of direct uptake and transport of LH-RH from the ventricle to the hypophyseal portal system. However, the direct pathway appears at best to be of questionable physiological significance, since intraventricularly administered LH-RH was less potent in causing LH release than i.v. LH-RH, even though the latter was diluted by the systemic circulation.