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In summary, the studies suggest that: (1) Simultaneous and controlled constriction of the brachiocephalic and left subclavian arteries resulted in chronic femoral hypertension in seven dogs. (2) This hypertension is associated heniodynamically with an increase in cardiac index due mainly to an increased stroke volume. (3) The suggestion is made that the initiating mechanism for this type of experimental hypertension is a chronic decrease in endosinal pulse pressure.

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A chronic type of experimental hypertension has been produced in dogs by bilateral sinus area constriction. Hypophysectomy has a prolonged antihypertensive effect in dogs with persistent hypertension resulting from carotid sinus area constriction, while no decrease in mean arterial pressure is seen after hypophysectomy in normotensive control dogs. These findings suggest the possibility that altered hypophyseal function participates in the pathogenesis of this typ^ of hypertension.T HE experimental production of chronic hypertension in dogs by bilateral carotid sinus constriction has been reported by Wakerlin, Crandall, Frank, Johnson, Pom per, and Schmid.1 Their studies suggest that the persistent hypertension which follows may be initiated either by altered carotid sinus function or by a change in cerebral hemodynamics.1 ' 2 The pathogenesis of this type of chronic hypertension is unknown and the possibility exists that it may be due to some altered humoral mechanism. Studies of others indicate that hypophysectomy in normotensive dogs does not necessarily lead to a fall in mean arterial pressure 3 ' 4 and in the dog, hypophysectomy does not prevent development of a modest renal hypertension following renal artery constriction.5 It was our view that in dogs hypertensive after carotid sinus constriction, the finding of a consistent and chronic antihypertensive effect of hypophysectomy would suggest a pathogenic role for altered hypophyseal function. METHODSMongrel dogs of both sexes, generally weighing less than 12 Kg., were caged and fed the same standard diet. Each dog was allowed a period of one or more months of normotension, followed by bilateral carotid sinus constriction and a postoperative period of 3 or more months to allow for stabilization of the resulting hypertension. The bilateral carotid sinuses were constricted as described by Wakerlin 1 using the plastic clamps described 1 -2 and generously supplied to us by Dr. Wakerlin.After these dogs became hypertensive, they were hypophyseetomized and observed for periods of varying lengths. Nbrmotensive dogs, without prior carotid sinus constriction, were also hypophysectomized to observe the effect of complete hypophysectomy on their mean arterial pressure.Preoperatively the dogs were given 25 mg. of cortisone intramuscularly. Brain shrinkage was obtained by administering intravenously 50 ml. of 30 per cent glucose solution approximately 20 to 30 min. prior to surgery. Hypophysectomy was accomplished via a left transtemporal approach, following (in part) the principles of Gushing'. 0 The surgical technie was modified in that the entire pituitary was removed under direct vision by suction rather than with Gushing forceps.Glucose solution (30 per cent) was intravenously injected postoperatively to relieve increased intracranial pressure during the 24 hours immediately following surgery. Small maintenance doses of either prednisolone or cortisone (usually 12 mg. every third day, intramuscularly) were given. Postoperative therapy included antibiotics. Dogs in...