A comparison of growth regulation of mammalian with amphibian lens epithelium.

In frogs hypophysectomy causes cell proliferation in lens epithelium to subside entirely, with better than 95% of the cells arresting in G1. The phenomenon has been traced to the action of insulin-like growth factors (IGFs) whose synthesis depends on anterior pituitary hormones, most notably GH. Both GH and purified somatomedin C can reinitiate mitosis in the lenses of hypophysectomized frogs. The present studies were done to determine if growth of rat lenses is controlled as is that of amphibia. It appears this may not be so because hypophysectomy has no effect on division in the rodent system. Protein calorie malnutrition (PCM) reduced the mitotic index and this effect is much enhanced by pituitary ablation. Of interest too, were the observations that the glucocorticoid, dexamethansone, is inhibitory in frog; the effect in rat is uncertain. Injection of bovine pituitary powder has no influence on rat while stimulating the amphibian material. It is therefore possible to modify growth of rat lens epithelium in vivo but the regulating mechanism(s) appears to be distinct from that operating in frogs. Whether the difference(s) is inherent in the cells themselves or is to be sought in the access routes through which they are reached by blood borne factors (e.g. permeability of blood-aqueous barriers) is, at present, unclear.