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I. Swenne, C. J. Crace and L. Jansson

ABSTRACT

The effect of a limited period of protein–calorie malnutrition in young rats on insulin secretion in the adult has been studied. Three-week-old rats were weaned onto diets containing 5% protein (low protein; LP) or 15% protein (control; C) and maintained for 3 weeks on their respective diets. A third experimental group was weaned onto standard rat chow (18% protein; normal diet; N). From 6 weeks of age onwards all rats were fed the standard rat chow. Pancreatic islets were isolated from rats aged 3, 6 and 12 weeks and their insulin secretory response to glucose or arginine was tested. At 12 weeks the effects of the secretagogues were also tested using perfusion of isolated pancreatic glands.

In islets from 6-week-old LP rats the glucose-stimulated insulin release was only 25% of that of C and N rats of the same age. Islets from C and N rats responded to arginine in the presence of a low glucose concentration with a small increase in insulin secretion, whereas no such response could be demonstrated in islets from 6-week-old LP rats. Islets from 6- and 12-week-old N rats responded to glucose and arginine. Islets from 12-week-old C rats had a similar response to glucose but did not respond to arginine in the presence of a low glucose concentration. In islets from 12-week-old LP rats the secretory response to glucose remained only 40% that of C and N rats and there was no response to arginine in the presence of a low glucose concentration. The observations on the secretory response of isolated islets from 12-week-old rats were paralleled by similar findings with the perfused, isolated pancreas.

It is concluded that protein–calorie malnutrition early in life persistently impairs the insulin secretory response of the B cell. The individual may, as a consequence, have a lowered ability to respond to nutritional and diabetogenic challenges and it is thus possible that early protein–calorie malnutrition predisposes for diabetes.

J. Endocr. (1988) 118, 295–302

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L. Carlsson, S. Edén and J.-O. Jansson

ABSTRACT

The plasma GH levels of female rats during late pregnancy were determined using an automatic method for repetitive blood sampling from conscious animals. The plasma GH patterns were analysed by a pulse analysis computer program (PULSAR). The mean plasma GH levels were about twofold higher in pregnant females on days 15, 18 and 22 of gestation than in age-matched non-pregnant females. The basal plasma GH levels were also increased, while there was no change in GH pulse amplitude or frequency. The augmentation of GH release was even more pronounced on day 20 of gestation, with a fourfold increase in mean plasma GH levels compared with those in non-pregnant females. This increase reflected an increase in both basal plasma GH levels and GH pulse amplitude, but there was no increase in pulse frequency. In female rats that delivered on day 22 of gestation, the basal and mean plasma GH levels increased during parturition.

Pregnant females consistently responded to multiple i.v. infusions of 1 μg human GH-releasing factor analogue (hGRF(1–29)-NH2) given at 45-min intervals on day 18 of gestation. Both basal and GRF analogue-stimulated plasma GH levels were undetectable after hypophysectomy of pregnant rats.

The present study demonstrates an increase in basal plasma GH levels during late pregnancy and a marked increase in both basal plasma GH levels and GH pulse amplitude on day 20 of gestation. Furthermore, hypophysectomy of pregnant rats results in undetectable GH levels, indicating that the high levels of GH during pregnancy are derived from the pituitary.

Journal of Endocrinology (1990) 124, 191–198

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L. Ohlsson, O. Isaksson and J.-O. Jansson

ABSTRACT

The influence of endogenous gonadal steroids in male and female rats on basal and growth hormone-releasing factor (GRF)-stimulated GH secretion from perifused anterior pituitaries was studied. After 75 min of perifusion with basal medium, freshly dissected pituitaries were exposed to human GRF(1–44) (10 nmol/l) for 15 min. Neonatal (day 1–2) or prepubertal (day 25) gonadectomy of male rats suppressed baseline GH release (ng/min per mg dry weight) as well as GRF-stimulated GH release by 40–70%. This effect was slightly more pronounced in neonatally gonadectomized animals. In prepubertally gonadectomized male rats, the suppression of GH release was completely reversed by testosterone replacement therapy. In female rats, prepubertal gonadectomy did not affect GH secretion from perifused pituitaries. However, treatment of ovariectomized female rats with oestradiol reduced baseline and GRF-induced GH release to levels lower than those observed in sham-operated or vehicle-treated ovariectomized animals. The data suggest that testicular androgen secretion in adult male rats increases the pituitary GH release in response to GRF in vitro, whereas ovarian oestrogen secretion is of less importance for the GRF responsiveness of female rat pituitaries.

J. Endocr. (1987) 113,249–253

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A M Svensson, C Hellerström and L Jansson

Abstract

The aim of the present study was to evaluate the effects of diet-induced obesity on pancreatic islet blood perfusion in normal Wistar rats. Furthermore, we investigated to what extent any obesity-associated changes in islet blood flow could be reversed after reversion to a normal diet with normalization of body weight. Young adult female Wistar rats were offered a palatable mixed high-caloric diet (cafeteria diet) in addition to standard pelleted chow. Age-matched control rats received standard pelleted chow only. After 4 weeks the diet-treated rats had a body weight of approximately 15% more than that of the controls. All diet-treated rats had decreased glucose tolerance and increased serum insulin concentrations, but basal blood glucose concentrations were similar in anesthetized diet-treated and control rats. Whole pancreatic and islet blood flow rates were measured with a microsphere technique. The islet blood flow as well as fractional islet blood flow were increased (P<0·01) in rats fed the cafeteria diet, while blood perfusion of the whole pancreas was similar to that of the control rats. In a second experiment, rats received the cafeteria diet for 4 weeks and were then fed standard pelleted food alone for another 3 weeks, while controls received standard diet for 7 weeks. After this period total body weight, retroperitoneal fat pad weight and glucose tolerance were similar to those of the controls. Whole pancreatic blood flow was unchanged as compared with that of control rats. However, both islet blood flow (P<0·01) and fractional blood flow (P<0·01) were increased. We conclude that diet-induced obesity in rats is associated with decreased glucose tolerance, hyperinsulinemia and a specific increase in absolute and fractional islet blood perfusion. This increase persists for at least 3 weeks after the diet is withdrawn despite normalization of body weight and glucose tolerance.

Journal of Endocrinology (1996) 151, 507–511

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AM Svensson, B Bodin, A Andersson and L Jansson

Increased blood perfusion of pancreatic islets is seen during various conditions of increased demand for insulin secretion. Pregnancy confers an increased need for insulin secretion, met by increased islet mass and volume as well as a decreased threshold for glucose-induced insulin secretion. In the present study, whole pancreatic and islet blood flow were studied with a microsphere technique in Wistar rats on days 15, 18 and 20 of pregnancy and days 2 and 7 post-partum. There were no changes in total pancreatic blood flow during pregnancy and the first post-partum week. Total blood perfusion through islet tissue expressed as flow per weight of whole pancreas was higher at day 15 of pregnancy. When islet blood flow was expressed per gram of islet tissue there was a decrease at day 18 of pregnancy. This decrease of islet blood flow was concomitant to a short-lived increase of the islet mass at the end of pregnancy. We conclude that upregulation of insulin output during late pregnancy does not specifically include increased net blood perfusion through the islets. One possible reason for this might be lack of synchronization between the proliferation of endocrine cells and angiogenesis, resulting in a relative decrease in islet vascular density in the islets.