Comparison of antihyperglycemic effects of creatine and metformin in type II diabetic patients.

PURPOSE: To compare the antihyperglycemic effects of metformin and creatine in recently detected type II diabetics in a short-term clinical study. METHODS: In a 14 day simmetrically randomized crossover study, recently detected type II diabetics received either creatine (2x3 g/day) or metformin (2x500 mg/day) for five days, followed by two days of washout, followed by cross-over to the opposite treatment for the next five days. Fasting and post-prandial (-15, 60, 90, 120, 180 and 240 min) blood glucose, insulin, c-peptide, creatine and lactate were measured every other day for the duration of treatment, and HbA1c only at the begining and at the end of the study. RESULTS: Both creatine and metformin decreased glucose concentrations to similar levels at all time points vs. basal glucose values [-15, 60, 90, 120, 180, and 240 min]: 11.1+/-0.75 vs 9.1+/-0.55a vs 8.8+/-0.59b, 14.4+/-0.6 vs 12.9+/-0.47a vs 13.1+/-0.55a, 14.8+/-0.58 vs 13.0+/-0.46b vs 13.3+/-0.55a, 14.1+/-0.6 vs 11.9+/-0.42b vs 12.5+/-0.51a, 12.2+/-0.6 vs 9.6+/-0.36c vs 9.9+/-0.38c, and 10.1+/-0.47 vs 7.8+/-0.36c vs 8.4+/-0.4b; (aP < 0.05; bP < 0.01; cP < 0.001 vs. basal glucose values). Neither treatment altered insulin, c-peptide, or HbA1c. Lactate varied during the day, but never reached the upper level of the safety reference range. CONCLUSION: Short-term treatment with creatine and metformin elicits similar glucose lowering effects in recently detected type II diabetics. Further studies are necessary to determine the effect of creatine on long-term glucose and insulin regulation.

Genetic consequences of a severe population bottleneck in the Guadalupe fur seal (Arctocephalus townsendi).

Population bottlenecks may lead to diminished genetic variability and correlative effects on fitness. The Guadalupe fur seal was nearly exterminated by commercial sealers during the late 18th and early 19th centuries. To determine the genetic consequences of this population bottleneck, we compared the variation at a 181 bp section of the mitochondrial DNA (mtDNA) control region from the bones of 26 prebottleneck fur seals versus variation in the extant population. We found 25 different mtDNA genotypes in the prebottleneck fur seals and only 7 genotypes among 32 extant fur seals, including only one of the ancient genotypes. These data demonstrate a substantial loss of genetic variability correlating with the recent population bottleneck. We also found from several genetic measures that the prehistoric population of Guadalupe fur seals was robust and that it had been increasing at some time during the late prehistoric period. Continued recovery of this species may, however, owe more to more immediate nongenetic factors, such as poaching and local availability of food resources during the breeding season and consequent effects on pup survival, than on the reduced genetic variability.

Enhanced relaxation to the rho-kinase inhibitor Y-27632 in mesenteric arteries from mineralocorticoid hypertensive rats.

Increased vasoconstriction is characteristic of hypertension. In this study, we tested the hypothesis that changes in vascular responses during mineralocorticoid hypertension may be due to increased activation of the Rho/Rho-kinase pathway. To test this, relaxation responses to the Rho-kinase inhibitor Y-27632 were determined by measuring isometric force in deendothelialized mesenteric arteries from mineralocorticoid-hypertensive rats and sham-operated controls. Following agonist-induced contraction by serotonin (5-HT, 5-hydroxytryptamine), arteries from hypertensive rats demonstrated a greater relaxation to the Rho-kinase inhibitor Y-27632 (65 +/- 5% vs. 28 +/- 10%). Treatment with an EC50 concentration of Y-27632 following a KCl-induced contraction caused minimal relaxation of arteries in both groups of animals. These findings suggest that augmented Rho-kinase activity in the vasculature of mineralocorticoid hypertensive rats may contribute to the enhanced vascular reactivity of agonist-mediated stimuli characteristic of this model of hypertension.

Angiotensin II AT1 receptors preserve vasodilator reactivity in skeletal muscle resistance arteries.

Resistance arteries (100-150 microm) were isolated from the gracilis muscle of normotensive Sprague-Dawley rats placed on a high-salt (HS) diet (4.0% NaCl) for 3-7 days. Exposure to the HS diet eliminated vascular relaxation in response to hypoxia (PO2 reduction to 35-40 Torr) and iloprost, a stable analog of prostacyclin. Vasodilator responses were restored in arteries isolated from chronically instrumented HS rats receiving a continuous intravenous infusion of either angiotensin II (ANG II; 5-6 ng x kg(-1) x min(-1)) or ANG II plus the AT2 receptor blocker PD-123319 (5 microg x kg(-1) x min(-1)) for 3 days before the isolated vessel studies. In contrast, coinfusion of the AT1 receptor blocker losartan (20 microg x kg(-1) x min(-1)) or coinfusion of both receptor blockers with ANG II eliminated the protective effect of ANG II to restore dilator responses to hypoxia and iloprost. Neither a HS diet nor ANG II infusion affected the dilation of gracilis arteries in response to direct activation of adenylyl cyclase by forskolin, suggesting that the effect of both the HS diet and the ANG II on the vasculature is mediated upstream from second messenger systems. These findings indicate that the protective effect of ANG II to maintain vasodilator reactivity in resistance arteries of rats on a HS diet is mediated via the AT1 receptor subtype.

An empirical genetic assessment of the severity of the northern elephant seal population bottleneck.

A bottleneck in population size of a species is often correlated with a sharp reduction in genetic variation. The northern elephant seal (Mirounga angustirostris) has undergone at least one extreme bottleneck, having rebounded from 20-100 individuals a century ago to over 175,000 individuals today. The relative lack of molecular-genetic variation in contemporary populations has been documented, but the extent of variation before the late 19th century remains unknown. We have determined the nucleotide sequence of a 179 base-pair segment of the mitochondrial DNA (mtDNA) control region from seals that lived before, during and after a bottleneck low in 1892. A 'primerless' PCR was used to improve the recovery of information from older samples. Only two mtDNA genotypes were present in all 150+ seals from the 1892 bottleneck on, but we discovered four genotypes in five pre-bottleneck seals. This suggests a much greater amount of mtDNA genotypic variation before this bottleneck, and that the persistence of two genotypes today is a consequence of random lineage sampling. We cannot correlate the loss of mtDNA genotypes with a lowered mean fitness of individuals in the species today. However, we show that the species historically possessed additional genotypes to those present now, and that sampling of ancient DNA could elucidate the genetic consequences of severe reductions in population size.

Novel signaling pathways contributing to vascular changes in hypertension.

In hypertension, increased peripheral resistance maintains elevated levels of arterial blood pressure. The increase in peripheral resistance results, in part, from abnormal constrictor and dilator responses and vascular remodeling. In this review, we consider four cellular signaling pathways as possible explanations for these abnormal vascular responses: (1) augmented signaling via the epidermal growth factor receptor to cause remodeling of the cerebrovasculature; (2) reduced sphingolipid signaling leading to blunted vasodilation and increased smooth muscle proliferation; (3) increased signaling via Rho/Rho kinase leading to enhanced vasoconstriction, and (4) a relative state of microtubular depolymerization favoring vasoconstriction in hypertension. These novel cell signaling pathways provide new pharmacological targets to reduce total peripheral vascular resistance in hypertension.

Elevated salt intake impairs dilation of rat skeletal muscle resistance arteries via ANG II suppression.

Vasodilator responses were assessed in resistance arteries (100-200 microm) isolated from the gracilis muscle of normotensive rats after changes in dietary salt intake. Sprague-Dawley rats were maintained on either a high-salt (HS) diet (4.0% NaCl) or a low-salt (LS) diet (0.4% NaCl) for 4-8 wk (chronic) or 3 days (short-term) with water ad libitum. One group of short-term HS rats received a continuous intravenous infusion of a low dose (5 ng x kg(-1) x min(-1)) of ANG II to prevent the ANG II suppression that occurs with HS diet. Short-term and chronic HS diet eliminated arterial dilation in response to ACh and reduced PO(2) (30-40 mmHg) and the stable prostacyclin analog iloprost. ANG II infusion preserved the response to these vasodilator stimuli in short-term HS animals. Dilator responses to sodium nitroprusside and forskolin were unaffected by HS diet. These findings suggest that ANG II suppression during HS diet impairs vascular relaxation mechanisms upstream from the cAMP and cGMP second messenger systems.

Chronic captopril administration decreases vasodilator responses in skeletal muscle arterioles.

Changes in arteriolar reactivity to dilator agonists were assessed in the cremaster muscle of Sprague-Dawley rats fed normal rat chow with captopril (100 mg/kg/day) in the drinking water for 8 weeks and in nontreated controls. The in situ cremaster muscle was prepared, superfused with physiologic salt solution, and arteriolar diameter was measured using television microscopy. Changes in the diameter of distal arterioles in response to topical application of iloprost, forskolin, cholera toxin, acetylcholine, and nitroprusside were measured with a video micrometer. Arteriolar responses to each of the vasodilator agonists used in this study were significantly reduced in the captopril-treated rats, relative to the untreated controls. The maximum dilation of the arterioles, determined during superfusion with Ca2+-free physiologic salt solution containing 10(-4) mol/L adenosine, was also reduced in the captopril-treated rats, suggesting structural remodeling of the arteriolar wall. These observations indicate that chronic angiotensin converting enzyme inhibition with captopril leads to significant alterations in arteriolar structure and reactivity, and that angiotensin II may play a protective role in maintaining normal vascular structure and vasodilator reactivity in the microcirculation.