Correlation of LH, FSH and GnRH release during various brain-pituitary coincubations

Hemipituitaries and various brain fragments from female albino rats were coincubated in the presence or absence of veratrine (a depolarizing agent). The release of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and gonadotropin-releasing hormone (GnRH) was measured by radioimmunoassay. In the absence of veratrine, none of the brain fragments affected LH and FSH release. In the presence of veratrine, large increases in LH and FSH release were caused by medial basal hypothalamic (MBH) fragments, slight increases were caused by suprachiasmatic:preoptic area fragments, and cerebral cortex fragments had no effect. LH and FSH release caused by brain fragments was significantly correlated with GnRH release and the GnRH concentrations attained during coincubations could account for all increases in LH and FSH release observed. Also, GnRH antiserum completely blocked increases in LH and FSH release during MBH-hemipituitary coincubations. The data indicate that the rat brain is unlikely to contain neurohormones other than GnRH capable of directly stimulating LH and FSH release in vivo.