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S. SYKES, L. M. MORGAN, J. ENGLISH, and V. MARKS

A rat intestinal perfusion technique has been used to assess the ability of a number of monosaccharides, monosaccharide analogues and disaccharides to stimulate intestinal release of immunoreactive gastric inhibitory polypeptide (GIP).

Perfusates containing glucose, sucrose, galactose, maltose, 3-O-methylglucose or α- or β-methylglucoside at concentrations of 100 mmol/l in Krebs–Ringer phosphate buffer (KRP) produced significant stimulation of GIP release compared with the control perfusions with KRP alone (P < 0·02). Mannose, 6-deoxygalactose, 2-deoxyglucose, myoinositol, fructose or lactose (100 mmol/1 of each) did not stimulate GIP release compared with controls. There was no significant difference in the ability of sucrose, maltose or β-methylglucoside (100 mmol/1 of each) to release GIP compared with 100 mmol glucose/1, but galactose, 3-O-methylglucose and α-methylglucoside (100 mmol/1 of each) produced significantly lower GIP responses than did glucose (P <0·02). Addition of 5 mmol phloridzin/1 to a perfusate containing 50 mmol glucose/1 prevented intestinal absorption of glucose and abolished the GIP response.

The molecular configuration of monosaccharides which have the ability to stimulate GIP release agreed well with the structural requirements for active transport by the sodium-dependent hexose pathway.

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C. S. Thompson, R. M. Sykes, J. Muddle, and M. R. Dashwood

ABSTRACT

In-vitro autoradiography was used to demonstrate the regional distribution of 125I-labelled insulin-binding sites in the liver, kidney and heart of normal rats and rats made diabetic with streptozotocin.

The distribution of insulin-binding sites in the liver of control rats was uniformly high, while in the kidney of control rats there was weak 125I-labelled insulin binding in the medulla and dense binding in the cortex. In the hearts of control rats a high density of 125I-labelled insulin-binding sites was evident both in the atrial and ventricular muscle.

Non-ketotic diabetes mellitus caused a marked increase in 125I-labelled insulin-binding sites in both the liver and kidney with the former tissue exhibiting a time-dependent (7 to 62 days) increase. There was no apparent effect of diabetes on insulin-binding sites in the heart.

Since experimental diabetes causes (1) a decrease in circulating insulin concentration and (2) impaired insulin action at many target tissues, the increase in 125I-labelled insulin-binding sites observed in the present study may represent a compensatory 'up regulation' of insulin receptors.

Journal of Endocrinology (1991) 128, 85–89