Immunoreactive 7B2 Concentrations in Plasma and Cerebrospinal Fluid in Pathophysiological Conditions and the Responses to Oral Glucose Load, Intravenous LH-RH, TRH and Arginine Infusion

Abstract

The peptide, 7B2, originally isolated from pituitary, has been shown to be present in endocrine tumors of high concentrations in pancreatic islet tumors. Plasma from most of these patients showed very high 7B2 immunoreactivity (IR-7B2) though there is a lack of knowledge concerning physiological and pathological changes in plasma IR-7B2 levels in other conditions. To assess whether or not there is any alteration in circulating IR-7B2 levels due to age, sex or any specific condition, plasma levels of IR-7B2 were measured in the fasting state in 106 healthy subjects aged 3 months to 91 years, 101 diabetics, 28 patients with hyperthyroidism. 7 patients with primary hypothyroidism, 13 patients with liver cirrhosis, 43 patients with chronic renal failure, 35 patients with cerebral vascular accident, and 26 pregnant subjects. Twenty-four cord bloods were also included. The responses of circulating IR-7B2 to oral glucose, intravenous arginine infusion, volus thyrotropin (TRH) or volus luteinizing hormone-releasing hormone (LH-RH) injection were also evaluated. Particularly high IR-7B2 levels were found to exist in cord blood. Postnatally the concentrations decreased gradually with age to adult values (15.6 +/- 2.9pmol/liter (mean +/- SE) in 20's-60's), though plasma IR-7B2 levels again increased significantly in over 70's (37.1 +/- 3.2pmol/liter; P less than 0.01). There was no significant difference in plasma 7B2 levels in either sex. Among the pathological conditions studied, significantly high IR-7B2 levels were observed in patients with chronic renal failure (175.1 +/- 35.9pmol/liter). Some of the pregnant patients in their third trimester also showed high plasma IR-7B2 levels. A small but significant rise in plasma IR-7B2 was observed after a glucose load in control subjects and diabetics. Intravenous LH-RH exerted a rise in plasma 7B2 concentrations though arginine and TRH showed no significant effect on plasma IR-7B2 concentrations. Compared with the plasma concentrations, ten to fifty-fold high levels of IR-7B2 were observed in cerebrospinal fluid (CSF) from patients with cerebrovascular accidents or multiple sclerosis. These results suggested that the kidney plays a major role in 7B2 degradation and that LH-RH simulates IR-7B2 release from the pituitary gland. Whether reduced clearance or increased production was responsible for the IR-7B2 elevation in subjects under 10 years or over 70 years requires investigation. Furthermore, high levels of IR-7B2 in CSF might indicate its specific role for the central nervous system.