Hormonal modification of the growth and metabolic effects of a transplantable rat insulinoma

Abstract. The growth and metabolic effects of a transplantable radiation-induced rat insulinoma were examined in intact male and female New England Deaconess Hospital (NEDH) rats, and in parathyroidectomised or adrenalectomised male NEDH rats. Subscapular transplantation of insulinoma fragments in intact male rats consistently produced a highly vascularised encapsulated tumour associated with hyperphagia, hyperinsulinaemia and hypoglycaemia which progressed to fatal neuroglycopaenic coma by 30 ± 0.8 days (mean ± sem) and 19 ± 0.5 days for slow-growing and fast-growing tumour sublines respectively (P <0.001). In intact female rats transplanted with the slow-growing subline, the onset of hyperphagia was advanced by 4 days and the severity of hyperinsulinaemia and hypoglycaemia increased (21% and 36%; P < 0.01 and P < 0.001, respectively), resulting in a 10% decrease of survival time (P < 0.05) and a 65% reduction of tumour weight (P < 0.01). Transplantation of the fast-growing subline into parathyroidectomised male rats, which exhibited a 15–24% (P < 0.05 – < 0.01) decrease of plasma calcium, did not modify either the growth or metabolic effects of the tumour. In contrast, transplantation of this subline into adrenalectomised male rats decreased survival time by 32% (P < 0.001) and reduced final tumour weight by 88% (P < 0.02) without markedly affecting the onset or magnitude of the hyperinsulinaemia. These results indicate that the growth and metabolic effects of the transplantable NEDH rat insulinoma are modified by the presence of ovarian hormones and by adrenal hormones. However, plasma calcium homeostasis after parathyroidectomy did not disrupt the growth and metabolic effects of this tumour.