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Studies on over fifty squirrel monkeys have revealed the prevalence of an imbalance of carbohydrate metabolism. Nearly half of the colony of adult female monkeys were found to exhibit both abnormal glucose tolerance and diagnostic tolbutamide curves when maintained on a standard commercial diet and under satisfactory laboratory conditions. The impaired monkeys commonly demonstrated normal fasting blood sugar levels and were without overt symptoms of diabetes, although occasionally frank symptoms of hyperglycemia and glucosuria were found in the colony. Several impaired animals responded to treatment with oral tolbutamide with apparent restoration of normal carbohydrate metabolism, but tolbutamide treatment did not improve the glucose tolerance of others. Although prevalence of atherosclerosis exists also in adult squirrel monkeys, no correlation of serum cholesterol and nonesterified fatty acids was found between normal monkeys and animals with carbohydrate impairment. DIABETES 16: 395-401, June, 1967. A previous report from this laboratory has noted the prevalence among normal squirrel monkeys (Saimiri sciureus) of an abnormality of carbohydrate metabolism evidenced by an impaired response to a modified standard oral glucose tolerance test. 1 The incidence and severity of this metabolic impairment was observed to be related to the sex and age. The highest incidence of animals with decreased carbohydrate tolerance occurred in the adult, although the carbohydrate intolerance exhibited even by this group was seldom severe enough to occasion glucosuria and it was only infrequently accompanied by elevated fasting glycemia. More recently, however, an occasional instance of diabetes has been discovered in the colony. Even though the natural occurrence of diabetes mellkus has been reported in a variety of animal species, 2 ' 3 it has been observed only rarely From the

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PERCENTAGE CHANGE IN DER IVATl VES 1OC 0 ACETY L ISOPROTERENOL STROPHANTHlDlN I FIG. 4. Percentage change in dP/dt and 8 P / d t 2 with infusion of acedyl strophanthich and isoproterenol. For acetyl strophanthidin, measurnmenits made at ninth minute of infusion of 100 microgramdmin. For iso.protereno1, measurements m d e at second minulte of infusion of 9 rnicrogrmdmin. Data presented a5 mean 2 SEM. Both derivatives in&asd significantly o v a the control d u e with isoprderenlol infusion; the increase in d'P/dt2 was significantly greater than dP/dt ( p < .05). With acetyl strolphamthiidin infusion, only dP/dt showed a significant increase over the control value ( p < .05>.action of digitalis on the myocardial contractile apparatus differs in some fundamental way from that of other inotropic stimuli. Summary.A new high fidelity fiberoptic pressure catheter has been used to measure the second derivative of left ventricular pressure, which constitutes an index of myocardial contractility. It may provide new information about the early phase of isometric ventricular contraction.A high prevalence of an impairment of carbohydrate metabolism is found in squirrel monkeys maintained on a standard commercial chow under controlled laboratory conditions ( 1 , 2 ) . The animals are asymptomatic of diabetes but exhibit abnormal diagnostic tol1butamide and glucose tolerance tests. Mertz and his co-workers have shown that progressive impairment of glucose tolerance associated with a diminished response of isolated tissues to insulin in vitro develops in rats and humans maintained on suboptimal in-*This study was supported in part by NIH grants FR-00180-01 a d CA-06474. take of trivalent chromium ( 3 ) . The metabolic defect was reversed by supplementation of trivalent chromium in drinking water or diet. Analysis ( 8 ) of the diet and drinking water of the squirrel monkeys revealed that the total chromium content was relatively low and of unknown valency state. The present investigation was undertaken to determine if the a b n o d diagnostic tolbutamide responses characteristic of metabolically impaired squirrel monkeys could be reversed and their glucose tolerance improved with chromium (111) dietary supplementation.Methods and Materials. The squirrel monkeys from the colony used in these experiments