Blood pressure effects of iontophoretically applied bioactive hormones in the anterior forebrain of the rat

In the course of electrophysiological investigations using iontophoresis, we observed that in specific regions of the forebrain even these minute applications of peptide and steroid hormones can influence systemic blood pressure. In urethan-anesthetized male Wistar rats, with a catheter in the femoral artery, iontophoretic application of the peptide hormones angiotensin II (ANG II), vasopressin (AVP), and atrial natriuretic peptide (ANP) and the steroid hormone aldosterone (ALDO) was effective at locations in the midline septum, the triangularis nucleus of the septum, and the subfornical organ (SFO). Increases in blood pressure (of up to 15 mmHg) were observed after ANG II and AVP, decreases after ALDO, and either an increase or a decrease, depending on the location, after ANP. There was no clear evidence of an antagonistic effect of ANP on ANG II-induced neuronal or blood pressure responses. In addition to demonstrating the potency of these hormones even when they are restricted to tiny volumes of tissue, the present results demonstrate that the medial ventral region of the anterior forebrain may be included in the same baroreceptive circuit as the SFO (and organ vasculosum of the lamina terminalis) and hence be involved in the regulation of blood volume and perhaps in the sensing of and corrective responses to extracellular thirst.