Immunoreactive substance P in the tubero-hypophyseal system of the rat: selective decrease in the neural lobe after dehydration and sodium loading.

In the tubero-hypophyseal system of the rat the approximate concentrations of immunoreactive substance P (I-SP), expressed as fmol/mg tissue, were 100 in the medial basal hypothalamus (MBH), 20 in the anterior lobe (AL), 20 in the neural lobe (NL) and 4 in the intermediate lobe of the hypophysis. These values were not altered by treatment with capsaicin on day 2 after birth. In rats in which the secretion of neurohormones from the NL was increased by dehydration followed by sodium loading there was a fall by 70% in the I-SP concentration of the NL; no change occurred in the AL or the MBH.