Hypothalamic stimulation induces vagally mediated hypocalcemia in the rat

To elucidate hypothalamic involvement in blood calcium homeostasis, the effects of unilateral electrical stimulation (0.1 mA, 0.5 ms, 30 Hz, 60 min) of the lateral hypothalamic area (LHA), the paraventricular nucleus (PVN), and the ventromedial nucleus of the hypothalamus (VMH) on the blood concentration of ionized calcium were examined in the anesthetized rats. LHA stimulation induced a sustained decrease (0.05-0.07 mM fall) in the blood calcium level during the period of 60 to 150 min (end of the measurements) after stimulation. In contrast, PVN stimulation elicited a transient hypocalcemia (0.07 mM decrease) 60 min after stimulation. The hypocalcemic effects of LHA and PVN stimulation were eliminated by vagotomy of the gastric branches and the thyroid/parathyroid branches, respectively. VMH stimulation, using the same parameters, did not induce any significant change in blood calcium. The results suggest that the LHA and the PVN have a hypocalcemic function that is mediated, at least in part, by the vagus nerve innervating the stomach and the thyroid/parathyroid glands, respectively.