Ultracentrifugation evidence for a somatostatin-binding protein in serum.

Using a technique of high speed centrifugation of serum and a well validated immunoassay for the measurement of serum somatostatin-like immunoreactivity, we have demonstrated that somatostatin, unlike other peptide hormones, appears to sediment with large molecular weight proteins. When synthetic somatostatin of increasing concentration was incubated with serum prior to ultracentrifugation, a linear plot of concentration of somatostatin added against concentration sedimenting (or apparently bound to protein) revealed an association curve. These data provide further evidence for the existence of a serum-binding protein for somatostatin.

The characterization of somatostatin-like immunoreactivity in human serum.

We describe the characterization of somatostatin-like immunoreactivity (SRIF-LI) found by radioimmunoassay (RIA) to be present in normal human serum. Degradation by serum of 125I-Tyr1 SRIF in the assay, as assessed by chromatoelectrophoresis and immunoprecipitation, was overcome by using EDTA in the assay buffer and Trasylol in the blood samples. Serum samples thus obtained from 48 normal subjects revealed a bimodal distribution of SRIF-LI; 92 per cent (group 1) had a mean level of 0.274 +/- 0.009 ng. per milliliter. What was measured in these sera showed identity to synthetic SRIF on serial dilutions, Sephadex G-25 chromatography, and thin-layer chromatography, and it was shown to be immunoreactive by an antibody-Sepharose affinity system. Higher levels (1.0 +/- 0.041 ng. per milliliter) were found in 8 per cent of the sera; 50 per cent of this material behaved identically as serum SRIF-LI from group 1. The remainder proved to be heterogeneous, consisting of two peaks of large molecular weight, both of which shared immunologic identity with synthetic SRIF as shown by binding to the antibody-Sepharose affinity system. Their further nature is unknown.

Tissue and serum somatostatin-like immunoreactivity in fed, 15-h-fasted, and 72-h-fasted rats.

Somatostatin-like immunoreactivity (SLI) was measured in extracts of gastric antrum, colon, pancreas, and central nervous system, as well as in unextracted portal and inferior vena caval serum from fed, 15-h-fasted, and 72-h-fasted rats. No differences were found in SLI in the central nervous system of the three groups. However, striking variations were found in the gastrointestinal tract and pancreas; the antrum, colon, and pancreas of 15-h-fasted rats contained the least SLI, the content being significantly elevated in these three areas after feeding and after a 72-h fast. Portal serum levels were highest after feeding but lowest in 72-h-fasted rats, in spite of high intestinal and pancreatic SLI content in both. These tissue and serum differences suggest a physiologic role for SLI in nutrient homeostasis not only at tissue level, but also putatively as a hormone in the portal system.

Plasma gonadotropin and gonadotropin-releasing hormone levels after intranasal administration of gonadotropin releasing hormone.

Intranasal administration of gonadotropin hormone (GnRH) in doses ranging from 2-4 mg produced a consistently prolonged LH response in patients with secondary amenorrhea. In 4 cases, a delayed secondary rise occurred. A similarly prolonged FSH response was observed in the majority of patients. Six hours after intranasal GnRH, FSH and LH values were well above basal levels and were higher than those observed at a similar interval after intravenous GnRH. Plasma GnRH levels after intranasal administration failed to achieve the high peaks found after the intravenous route but maintained elevated levels for at least an hour and often longer. Despite the much lower plasma GnRH levels, intranasal GnRH produced a sustained effect on LH and FSH secretion, greater than GnRH given by the intravenous route.

Disappearance rates of plasma growth hormone after intravenous somatostatin in renal and liver disease.

Plasma immunoreactive growth hormone (hGH) was measured before, during and after the administration of intravenous somatostatin to 3 patients with chronic renal failure and 4 with severe liver disease who had elevation of basal hGH. During somatostatin infusion, the hGH levels declined acutely in a linear fashion when log hGH was plotted against time. Rather surprisingly, the plasma hGH half disappearance time (t 1/2) was 27 min and 18 min in liver and renal disease respectively. These values do not differ from data obtained on normal subjects using exogenous hGH, labelled or unlabelled. Control data on normal subjects using this technique are not available as it was not possible to measure subnormal levels of plasma hGH with the required precision. It is possible that our findings of plasma hGH T 1/2 in liver and renal disease within the normal range reported using exogenous hGH might suggest that high levels of plasma hGH found in these two diseases are primarily caused by hypersecretion rather than impaired clearance.

Prolactin responses to thyrotropin-releasing hromone in protein-calorie malnutrition.

Basal plasma prolactin (hPRL) concentration is low, but the response to thyrotropin-releasing hormone (TRH) is within the normal range, in children with protein-carlorie malnutrition (PCM) before treatment. Treatment results in increased basal hPRL concentration and an increased response to TRH. The above findings contrast with normal or high basal TSH and the normal or exaggerated response to TRH provocation in untreated PCM. The reason for this divergence is obscure.

Peripheral plasma somatostatin-like immunoreactive responses to insulin hypoglycemia and a mixed meal in healthy subjects and in noninsulin-dependent maturity-onset diabetics.

We have measured peripheral plasma immunoreactive somatostatin (SRIF-LI) in 10 healthy subjects and 10 noninsulin-dependent maturity-onset diabetics (NIDDM). The mean (+/-SE) basal level of SRIF-LI in NIDDMs of 185 +/- 27 was similar to that of 174 +/- 23.5 pg/ml in age-, weight-, and sex-matched healthy subjects. Insulin hypoglycemia of equivalent magnitude induced a 113 +/- 15.8 pg/ml increase in SRIF-LI 40 min after injection in healthy subjects and no significant change in the NIDDMs. Ingestion of a mixed meal induced a biphasic rise with a mean peak of 75 +/- 30 pg/ml above basal at 15 min and a later peak of 130 +/- 35 pg/ml above basal at 120 min in healthy subjects. In NIDDM, there was no significant rise above basal, and the differences were significant at 15 and 120 min. Our findings are compatible with deficient SRIF release in these NIDDM in whom the deficient SRIF secretion may contribute to the hyperglycemia.

Body weight and the pituitary response to hypothalamic releasing hormones in patients with anorexia nervosa.

Fifteen women with anorexia nervosa were studied before and after weight gain. Basal plasma thyroid stimulating hormone (TSH) and prolactin (PRL), and the responses of both these hormones to thyrotropin releasing hormone (TRH), were normal. Basal plasma luteinizing hormone (LH) and follicle stimulating hormone (FSH) were low in patients who were emaciated, and their responses to gonadotropin releasing hormone (GnRH) were impaired. Both basal and stimulated levels of LH and FSH rose with weight gain, with a linear correlation between gonadotropin levels and body weight expressed as a percentage of standard. The FSH response became greater than normal in patients who had regained weight to more than 70% of standard, while the LH response to GnRH was exaggerated in those who had regained weight to more than 80%. Basal plasma estradiol (E2) levels were low at first, but returned to within the normal range in patients over 80% of standard. Menstruation resumed in some patients after they had regained weight. The relationship between body weight and gonadotropin levels appears to be an important feature of the menstrual disturbance in anorexia nervosa. The restoration of a normal body weight is a prerequisite for the resumption of menstruation in this condition, but other as yet unidentified factors may also be involved.

Fasting blunts the TSH response to synthetic thyrotropin-releasing hormone (TRH).

Thyrotropin (TSH) responses to intravenous thyrotropin-releasing hormone (TRH) were studied in 9 men after 12 and 36-h fasts separated by more than a week and performed in random order. The TSH, basally and in response to TRH, was significantly lower after the 36-h fast compared to that after 12 h. The mechanism for this effect is not clear, but may be related to the altered hormonal or fuel status associated with prolonged fasting.

Sulphation factor (somatomedin activity) in experimental protein malnutrition in the rat.

In a rat model of protein malnutrition in which the failure of growth is a major feature, a low level of bioassayable sulphation factor activity was present in the serum, associated with normal levels of growth hormone and low insulin in the plasma. The administration of pharmacological doses of human or bovine growth hormone did not increase the amount of sulphation factor activity in the serum or the width of the tibial epiphyses in the protein-malnourished animals. The basal and serum-stimulated incorporation of 35SO2-4 into the costal cartilages of malnourished animals did not differ from that of controls, which suggests that the responsiveness of the end-organs was normal.

A phylogenetic study of sulphation factor activity in 26 species.

Somatomedin (sulphation factor) activity was measured in 26 species by a porcine cartilage bioassay. Although non-dialysable inhibitory factors were present in many species, sulphation factor activity was present in the sera of all the vertebrates studied but was absent from the invertebrates.

Generation of somatomedin activity in response to growth hormone and insulin from isolated perfused livers of normal and protein-malnourished rats.

The generation of somatomedin activity by isolated perfused livers was examined in protein-malnourished (4% casein diet) and well-nourished (controls, 20% casein diet) rats. There was significantly less somatomedin activity (measured by the porcine costal cartilage bioassay), after perfusion for 2 h, in the perfusates from the livers of malnourished rats both in hormone-free perfusates and perfusates containing hormones (10 microgram GH/ml, 1000 microunits insulin/ml or a combination of the two). A reduction in the somatomedin activity generated by the liver may be the mechanism responsible for the low serum level of somatomedin (in spite of raised or normal levels of growth hormone) in human or experimental protein malnutrition.

Tissue distribution of immunoreactive somatostatin in the South African clawed toad (Xenopus laevis).

Immunoreactive somatostatin is present in the brain, gut and pancreas of the South African clawed toad, but is absent from the skin, a rich source of many other brain-gut peptides.

The effect of alanine infusions on growth hormone, insulin, and glucose in protein-calorie malnutrition.

In view of the previously reported inverse correlation between the elevated serum growth hormone (HGH) and low alanine in children with protein-calorie malnutrition (PCM), 30-min alanine infusions were performed in five children with PCM and 12-hr infusions in four children before and after therapy. These infusions did not lower basal HGH or improve its glucose suppressibility in untreated PCM, excluding a feedback relationship between HGH and alanine. There was no insulinotropic effect during 30-min infusions, but an improved insulin response to glucose after the 12-hr alanine infusion was found in three of four children before therapy. Plasma glucose rose slightly during alanine infusion in three of five children before treatment, but the magnitude of change was small and the relevance unclear.

Virilization with diffuse involvement of ovarian androgen secreting cells.

A case is reported in which virilization of long duration and gradual progression was found in association with ovarian hyperthecosis and bilateral hilar cell lesions. The frequency occurrence of both masculinizing and nonmasculinizing ovarian tumors in association with ovarian hyperthecosis and polycystic ovaries is discussed.