Diencephalic efflux of calcium ions in the monkey during exercise, thermal stress and feeding

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Abstract
The diencephalon of the unanesthetized macaque monkey was radio-labeled with Ca2+ by a microinjection of 6-8 .mu.C 45Ca2+ into the 3rd cerebral ventricle through a permanently implanted cannula. Successive 5 min push-pull perfusions of the mid-line hypothalamic region with an artificial CSF were carried out at a rate of 28 .mu.l/min every 20 min. A washout curve of declining 45Ca2+ radioactivity was thus generated. When the monkey exercised strenuously on a special rowing machine to obtain highly palatable banana pellets, its body temperature rose sharply. As the monkey exercise, during a sequence of push-pull perfusions , the concurrent efflux of 45Ca2+ ions increased markedly in the corresonding samples of diencephalic perfusate. This enhanced activity of Ca2+ continued throughout a 30 min work period and persisted as long as the monkey''s temperature was elevated in the interval immediately following exercise. Exposure of the monkey''s trunk, between neck and thigh to cold air of 5.degree. C likewise augmented the amount of 45Ca2+ ions in the diencephalic push-pull perfusates; however, a similar exposure to air warmed to 35.degree. C failed to alter the pattern of 45Ca2+ efflux from the animal''s diencephalon. If a fasted monkey consumed only the banana pellets but was not exercised, the level of 45Ca2+ in the perfusate also increased transiently, just at the onset of feeding. A local change in calcium transport, binding or other cellular activity of the cation within the diencephalon could play an important role in the central mechanism underlying the set-point rise in a primate''s temperature which accompanies vigorous exercise. Apparently this cation functions in the diecephalic control of metabolic heat production and in the overall processes of energy metabolism, particularly in relation to feeding.