ADENOHYPOPHYSEAL VASOACTIVE-INTESTINAL-PEPTIDE AND NEUROPEPTIDE-Y RESPONSES TO HYPOTHYROIDISM ARE ABOLISHED AFTER ANTEROLATERAL DEAFFERENTATION OF THE HYPOTHALAMUS

We examined whether hypothyroidism-induced increases in the anterior p ituitary content of vasoactive intestinal peptide (VIP) and neuropepti de Y (NPY) are mediated by the hypothalamus. Male Sprague-Dawley rats were anesthetized and one of the following surgeries was performed: (1 ) sham thyroidectomy, (2) thyroidectomy, (3) thyroidectomy plus surgic al anterolateral deafferentation of the medial basal hypothalamus, or (4) thyroidectomy and sham deafferentation of the hypothalamus (knife was inserted but not rotated). Two weeks after surgery, animals were k illed and tissue samples collected for measurement of the anterior pit uitary VIP and NPY and plasma thyroid-stimulating hormone (TSH), thyro xine, and prolactin concentrations (by RIA). Reverse-phase HPLC showed that VIP and NPY immunoreactivities in the anterior pituitary extract s are eluted in the positions identical to synthetic VIP and NPY, resp ectively. Only data from those animals with complete symmetric cuts lo cated at the posterior border of the optic chiasm were included for an alysis. In the thyroidectomized rats the anterior pituitary contents o f VIP and NPY were significantly increased. These responses were almos t completely prevented by the anterolateral deafferentation of the hyp othalamus. Sham hypothalamic deafferentation had no effect on the pitu itary neuropeptide responses to hypothyroidism. Anterolateral deaffere ntation of the hypothalamus also significantly blunted plasma TSH resp onses to hypothyroidism. These data suggest that some hypothalamic fac tor is involved in the mediation of the effect of hypothyroidism on th e pituitary content of VIP and NPY.