The experimental findings reported here may have some implications concerning the secretion of insulin under physiological conditions. They would suggest that at agiven level of blood glucose, the rate of insulin loss from the beta cells may be largerwhen the level of insulin in the blood is low. They would suggest too that beta cells lining the proximal portions of the islet sinusoids would secrete to a greater degree thanbeta cells lining the more distal parts of the sinusoids.
In previous experiments reported elsewhere (see reference 3) it could not be demonstrated satisfactorily that large amounts of beef insulin (30 U.) added to solutions of glucose inhibited the rate of degranulation of beta cells of the infused rats. The results of those experiments and the results with insulin-antibody, reported here, need to be reconciled. Excess circulating insulin-antibody probably keeps the concentration of free diffusible insulin at levels close to zero in the sinusoids of the islets. The mechanism facilitating beta cell degranulation may be operating effectively at extremely low concentrations of insulin. Maximal inhibition of the glucose effect may be reached very soon as the concentration of diffusible insulin rises in the sinusoids of the islets. In ratsinfused with glucose, endogenous insulin in the milieu of the beta cells might quickly reach this level so that the addition of exogenous beef insulin has no demonstrable effect.