Studies of glucagon resistance in large rat adipocytes: 125I-labeled glucagon binding and lipolytic capacity.

This study is concerned with potential modifications of large fat cells from adult rats (400-450 g) that make them resistant to stimulation by glucagon. The lipolytic capacity and (125)I-labeled glucagon-binding capability of these cells were compared with these properties of small glucagon-sensitive cells from young rats (130-160 g). As determined by maximal stimulation with theophylline, dibutyryl cAMP, or epinephrine, the lipolytic capacity of large cells was not markedly different from small cells, which suggests that an alteration contributing to glucagon insensitivity is not present in the enzymes involved with hormone-mediated lipolysis.

Epidermal growth factor: receptors in human fibroblasts and modulation of action by cholera toxin.

Epidermal growth factor (EGF) stimulates both DNA and RNA synthesis in contact-inhibited human fibroblasts. Stimulation of DNA synthesis is observed at concentrations as low as 3 pM, is half-maximal at 70 pM, and is maximal at 300 pM EGF. The action of EGF is similar to that of fetal-calf serum, but is distinguished by the time-course of stimulation and by the ability of serum to stimulate further those cells maximally stimulated by EGF.

Binding of nerve growth factor receptor in sympathetic ganglia.

(125)I-Labeled nerve growth factor binds to membrane preparations from superior cervical ganglia of rabbit in a specific fashion indicative of an interaction with the physiological receptor. Of various tissues examined, binding was observed only in the superior cervical ganglia, a presumed target organ of nerve growth factor. Binding of labeled factor is displaced by nonradioactive factor but not by several other peptide hormones.

Guanosine 3':5'-cyclic monophosphate and the action of insulin and acetylcholine.

Low concentrations of insulin (120 muunits/ml) and of carbamylcholine (1 muM) increase cyclic GMP content in isolated fat cells by 350%. The maximal amount of cyclic GMP, achieved within 2 min after addition of insulin or carbamylcholine, falls rapidly for insulin and much more slowly for carbamylcholine. 10 pM Acetylcholine can also augment the content of fat-cell cyclic GMP, but by 5 min (37 degrees ) the amount falls to that of unstimulated cells.