Insulin promotes phosphorylation and activation of geranylgeranyltransferase II. Studies with geranylgeranylation of rab-3 and rab-4.

Rab proteins play a crucial role in the trafficking of intracellular vesicles. Rab proteins are GTPases that cycle between an inactive GDP-bound form and an active GTP-bound conformation. A prerequisite to Rab activation by GTP loading is its post-translational modification by the addition of geranylgeranyl moieties to highly conserved C-terminal cysteine residues.

Medullary carcinoma of the thyroid before age 2 years.

An 18-month-old infant was evaluated for medullary thyroid carcinoma (MTC) because of a maternal history of the tumor and the presence of characteristic mucosal abnormalities. Although examination of the thyroid gland was normal, RIA of plasma calcitonin reveled elevated basal levels of the hormone and the patient underwent total thyroidectomy at 23 months of age. Histological examination of the tumor was consistent with the diagnosis f MTC, and this diagnosis was confirmed by immunohistology.

Factitious hypoglycemia. Diagnosis by measurement of serum C-peptide immunoreactivity and insulin-binding antibodies.

In seven patients with factitious hypoglycemia due to the surreptitious injection of insulin, we made the diagnosis by measurements of plasma insulin and C-peptide immunoreactivity (in seven patients), facilitated by the finding of circulating insulin-binding antibodies (in two patients). The simultaneous demonstration of low plasma glucose, high immunoreactive insulin and suppressed C-peptide immunoreactivity represents a triad of results pathognomonic of exogenous insulin administration. Determination of plasma free C-peptide and free insulin permitted patients with high titers of insulin antibodies, including those with a history of insulin-treated diabetes, to be studied and diagnosed in a way similar to that in subjects who had no circulating insulin antibodies.

Effects of alternating phosphorus and calcium infusions on osteoporosis.

The osteoblastic effect of inorganic phosphorus and the inhibitory action of calcium on parathyroid hormone secretion formed the basis for a therapeutic trial in which both elements were given intravenously in an alternating sequence for one year to five patients with severe osteoporosis. During treatment, calcium and phosphorus balances were positive, and serum phosphorus concentrations decreased. Iliac crest bone biopsy specimens obtained one year after beginning treatment demonstrated an increase in the thickness of cortical bone.

Clinical correlations of serum proinsulin-like material in islet cell tumours.

To examine the possibility that the concentration of circulating proinsulin-like material (PLM) might be helpful in evaluating the therapeutic response of patients with islet cell tumours, serum levels of PLM in three patients with islet cell tumours were correlated with hypoglycaemic symptoms and plasma glucose concentrations before and after treatment. In two patients ranges of fasting PLM concentration were 0.21-0.