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Intramuscular injections of aldosterone increased the urinary excretion of sodium and the rate of elimination of a water load by hypophysectomized rats. The sodium retaining action of aldosterone could, however, be restored in these animals either by the administration of growth hormone, or by adrenalectomy, or by removal of that part of the diencephalon which underlies the pineal stalk (Lockett & Roberts, 1963a).The present work is a study of the modification of the renal effects of growth hormone by hypophysectomy in rats. METHODSFemale Wistar rats, 140-180 g, drank freely and were fed on diet 86 (M.R.C. Animal Laboratory Bureau, 1952); this was crushed and was made into a stiff mash for all hypophysectomized animals. The drinking water supplied to adrenalectomized animals contained 0-6 % NaCl. All were maintained at a room temperature of 23-25°C.Operations were performed under light pentobarbitone anaesthesia, deepened with ether as necessary. The transpharyngeal route was used for hypophysectomy (Bum, 1952); a mid-dorsal incision was employed for adrenalectomy. The usual operation for total hypophy. sectomy was modified: the sharp edge of the capillary sucker was held against the adenohypophysis in such a way that approximately one-sixth of the adenohypophysis was cut off and remained detached within the pituitary fossa as the rest of the gland was removed. This small portion of the adenohypophysis presumably atrophied, for the adrenal weights fell to one third of normal in 3 weeks (Table 1). The advantages of this modification in technique were great, for adequate water diurises were sustained for long enough to permit the use of cross-over tests, from the fifth to the fifteenth day, for measurement of the effect of hormones. In this and the following paper, subtotal hypophysectomy implies that this operation was used. Neurohypophysectomy was effected by passing a fine capillary sucker through the right side of the adenohypophysis before very gentle suction was applied; this suction was just sufficient to remove the posterior lobe but almost always produced slight bleeding. Four weeks later, however, these animals showed brisk responses to water loads, a fivefold increase in sensitivity to the antidiuretic hormone and a water intake greatly in excess of normal. All experiments were conducted during this phase, and ended in the middle of the third post-operative month. Sensitivity to the antidiuretic hormone had begun to decrease by the end of the third month, probably because that residual part of the pars nervosa which extends into the infundibular process had hypertrophied. These

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