Introduction: the clinical significance of peptide hormone receptors

The gastrin receptor assay

Gastrin is a major physiologic regulator of gastric acid secretion and growth of the oxyntic mucosa. Biologically active radiolabelled hormones may be used to characterize and localize receptors for peptide hormones. The cellular localization of the gastrin receptor in the fundic mucosa, however, is still a matter of great debate owing to difficulties in developing a gastrin receptor binding assay. Despite considerable work in several laboratories, the criteria for true receptor binding have not yet been fulfilled. The preparation of a suitable tissue receptor material (plasma membranes or isolated cells) from the heterocellular fundic mucosa seems to be the major problem. This problem may be related to the fact that the receptors are only present on the enterochromaffin-like cells (ECL), which constitute but a minor fraction of the cells in the oxyntic mucosa. Furthermore, the second messenger of gastrin is still not known, and the poor functional responsiveness of isolated cells and the oxyntic glands to gastrin further complicates the evaluation of the gastrin receptor. In this review the different steps in the gastrin receptor assay (the labelling of gastrin, preparation of the receptor, and the incubation and correlation of the binding and biologic effect of gastrin) are discussed.

Receptors in disease: an overview

Hormones and certain other signal molecules bind to plasma membrane or intracellular receptors producing signals that initiate their physiological effects. Recent understanding of receptors has resulted in recognition of several categories of receptor-related abnormalities. (a) Congenital receptor abnormalities such as receptor deficiency syndrome. LDL receptor defect in familial hypercholesteremia and primary androgen resistance are examples. (b) Postreceptor coupling abnormalities such as pseudohypoparathyroidism type Ia where there are reduced levels of guanine nucleotide receptor cyclase coupling protein. (c) Acquired receptor abnormalities, such as presence of circulating antireceptor antibodies. Such antibodies have been implicated in the pathophysiology of many diseases including Graves' disease and myasthenia gravis.

Plasma cortisol and aldosterone after ACTH 1-17: effect of different doses

In order to evaluate the effects in adults of different doses of ACTH 1-17 on the cortisol and aldosterone secretion, 200 micrograms of ACTH 1-17 were injected i.m. at 07(00) in two groups of 6 patients each of both sexes. Sampling was done before and after ACTH 1-17 administration at 4-h intervals from 08(00) to 04(00) in order to define the circadian profiles of both cortisol and aldosterone. At the time of study all subjects were kept under the same routine conditions. The i.m. injection of 100 micrograms of ACTH 1-17 was followed by a maximum response of cortisol which coincided with the physiological circadian peak of the hormone (511.7 +/- 122.7 vs 195.5 +/- 92.9 ng/ml; mean +/- 1 SD; p less than 0.001). With this treatment no variations in the normal circadian rhythm were observed. After the injection of 200 micrograms ACTH 1-17, a marked variation in the circadian rhythm of cortisol (peak at 16(00): 390.0 +/- 49.8 ng/ml; mean +/- 1 SD) was observed. Significant variations in the circadian rhythm of aldosterone with respect to the normal profile were observed only after the injection of 200 micrograms ACTH 1-17 (peak at 16(00): 137.5 +/- 50.5 vs 50.8 +/- 36.1 ng/ml; mean +/- 1 SD; p less than 0.01). The hormone increase observed after the injection of 100 micrograms (peak at 08(00): 111.7 +/- 87.5 vs 61.3 +/- 16.5 ng/ml; mean +/- 1 SD) was not statistically significant. Our results indicate that the clinical use of ACTH 1-17 i.m. is not recommended at doses greater than 100 micrograms.(ABSTRACT TRUNCATED AT 250 WORDS)