Blockde of volume expansion-induced release of atrial natriuretic peptide by median eminence lesions in the rat

Since stimulation of the anteroventral third ventricle region (AV3V) induced a rapid elevation of plasma atrial natriuretic peptide (ANP) associated with rapid changes in brain and pituitary content of ANP, whereas lesions of the AV3V were followed by marked by a merked decline in plasma, brain and pituitary content of the peptide, we hypothesized that release of ANP from the median eminence (ME) might be an important pathway to control plasma ANP. Consequently, electrolytic lesions were placed in the ME and the response to hypertonic-expansion was determined in conscieous rats. In sham-operated controls volume expansion produced a 3.5-fold increase in plasma ANP concentrations within 5 min. Values rapidly declined to enar initial levels at 15 and 30 min. Median eminence lesions almost completely blocked the response to volume expansion at 24 and 120 h post-lesion and initial anp concentrations were lower than those of the sham-operated controls. The results indicate that increased release of ANP from the neurohypophysis may play an important role in the increased plasma ANP concentrations whic follow volume expansion

Release of alpha-MSH from the in vitro superfused neuro-intermediate lobe of the pituitary of the rat by antidiuretic hormone.

The effect of antidiuretic hormone (ADH) on the release of immunoreactive alpha-melanocyte stimulating hormone (alpha-MSH) from the superfused neurointermediate lobe of the pituitary of the normal Wistar and Brattleboro (diabetes insipidus) rat was studied in vitro. In control experiments, there was usually an initial peak, after which alpha-MSH release fell exponentially over the course of the perfusion. Following the addition of ADH, the levels of alpha-MSH in the superfusate showed a significant rise. It is suggested that ADH is normally involved in the secretion of alpha-MSH by the pars intermedia of the rat, especially in response to osmotic stimuli.