[Serum and plasma insulin levels in zinc-deficient rats following glucose stimulation]

In three experiments male Sprague-Dawley rats depleted in zinc (2 ppm dietary zinc) for 30 to 35 days had greatly reduced serum insulin levels when compared to ad libitum-fed control animals (100 ppm dietary zinc) but in only one of the experiments when compared to pair-fed control animals (100 ppm dietary zinc) which also had reduced insulin levels. Similarly, in a following study the plasma insulin levels of zinc-deficient animals depleted for 20 days were not different from those of pair-weight control animals (100 ppm dietary zinc). Fifteen minutes after one i.m. glucose injection and 15 minutes after two glucose injections, two hours apart, the zinc-deficient rats showed a higher blood glucose level than the pair-weight controls. The plasma insulin contents also increased after the glucose stimulation but were not significantly different between the zinc-deficient and the zinc-supplemented groups. It is assumed that zinc deficiency lowers the physiological potency of insulin and thereby effects a reduced glucose homeostasis of zinc-deficient rats. This could also be demonstrated by additional studies with zinc-deficient rats which secreted 76 per cent more insulin after a Rastinon injection than control animals though they showed about the same bloodglucose levels.