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E. B. SMALSTIG, C. J. SHAAR, D. R. BENNETT, J. G. POWELL JR, and R. L. COCHRANE

Rat dams were ovariectomized on day 3 of pregnancy and treated with corn oil (0·25 ml/day), progesterone (4 mg/day), cortisone acetate (2 or 10 mg/day), cortisone acetate (10 mg/day) plus progesterone (4 mg/day) or progesterone (4 mg/day) plus oestrone (1 μg/day) from days 2 to 8 or 14, followed by 6 to 11 days of treatment with progesterone (4 mg/day) plus oestrone (1 μg/day). Implantation of ova at the normal time was realized in the animals treated from day 2 with progesterone plus oestrone. Implantation of ova was only realized subsequent to progesterone plus oestrone in the dams treated with progesterone alone, cortisone acetate alone, or progesterone plus cortisone acetate, except for one animal in the latter group. Implantation of ova was not usually realized even after progesterone plus oestrone treatment in the dams treated with corn oil. Even though cortisone acetate maintained unimplanted ova in spayed rats in much the same manner as does progesterone, it was not equivalent to progesterone in efficacy or action.

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P. R. Flatt, M. G. DeSilva, S. K. Swanston-Flatt, C. J. Powell, and V. Marks

ABSTRACT

The effects of repeated s.c. transplantation of clonal insulin-secreting RINm5F cells in NEDH rats on tumour morphology, insulin–glucose homeostasis and the function of RINm5F cells re-established in culture were examined after maintenance in vivo for periods of up to 308 days. Transplantation of RINm5F cells for ten consecutive passages consistently produced a single encapsulated vascularized tumour associated with the development in recipient rats of hyperinsulinaemia, hypoglycaemia and eventual neuroglycopenic coma. At the tenth passage, tumour-bearing rats exhibited a markedly enhanced rate of insulinstimulated glucose uptake by 19 days, with evidence of a large and variable insulin response to i.p. glucose. Survival was 22 ± 2 days, and resected RINm5F cell tumours exhibited weak immunostaining for insulin in scattered cells, with strands of fibrous tissue separating clusters of tumour cells many of which had distinct polarity. There was no detectable immunostaining for glucagon, somatostatin or pancreatic polypeptide. The insulin content and insulin secretory output of RINm5F cells re-established in culture after 20, 146, 259 or 308 days propagation in vivo were generally enhanced compared with non-passaged RINm5F cells. The magnitude of the effect was not appreciably affected by the duration of maintenance in vivo, but it was critically dependent upon the subsequent period of culture in vitro. Thus, whereas 2-day cultured RINm5F cells from the eighth tumour passage exhibited a greater than 100–fold increment of insulin content and release, with enhanced secretory responsiveness to leucine, arginine, theophylline, K + (25 mmol/l) or Ca2+ (7·6 mmol/l), RINm5F cells cultured for a further 19 days had almost completely lost the attributes resulting from 259 days of maintenance in vivo. The results indicate substantial enhancement of the functional capabilities of RINm5F cells in vivo, and suggest that the resulting tumours afford a novel model in NEDH rats of responsive trabecular-type insulinomas.

J. Endocr. (1988) 118, 429–437