Effects of prior exercise on insulin-mediated and noninsulin-mediated glucose uptake in horses during a hyperglycaemic clamp

Insulin Sensitization Following a Single Exercise Bout Is Uncoupled to Glycogen in Human Skeletal Muscle: A Meta-analysis of 13 Single-Center Human Studies

Exercise profoundly influences glycemic control by enhancing muscle insulin sensitivity, thus promoting glucometabolic health. While prior glycogen breakdown so far has been deemed integral for muscle insulin sensitivity to be potentiated by exercise, the mechanisms underlying this phenomenon remain enigmatic. We have combined original data from 13 of our studies that investigated insulin action in skeletal muscle either under rested conditions or following a bout of one-legged knee extensor exercise in healthy young male individuals (n = 106). Insulin-stimulated glucose uptake was potentiated and occurred substantially faster in the prior contracted muscles. In this otherwise homogenous group of individuals, a remarkable biological diversity in the glucometabolic responses to insulin is apparent both in skeletal muscle and at the whole-body level. In contrast to the prevailing concept, our analyses reveal that insulin-stimulated muscle glucose uptake and the potentiation thereof by exercise are not associated with muscle glycogen synthase activity, muscle glycogen content, or degree of glycogen utilization during the preceding exercise bout. Our data further suggest that the phenomenon of improved insulin sensitivity in prior contracted muscle is not regulated in a homeostatic feedback manner from glycogen. Instead, we put forward the idea that this phenomenon is regulated by cellular allostatic mechanisms that elevate the muscle glycogen storage set point and enhance insulin sensitivity to promote the uptake of glucose toward faster glycogen resynthesis without development of glucose overload/toxicity or feedback inhibition.

Glucose and insulin response after intravenous and subcutaneous somatostatin administration in healthy horses

Equine metabolic syndrome (EMS) is prevalent in the equine population, and somatostatin analogs might be useful for diagnosis and/or treatment of EMS in horses. The purpose of this study was to evaluate the glucose and insulin responses to subcutaneous and intravenous administration of somatostatin. Six healthy research horses were included in this prospective study. An initial pilot study was performed to assess several different doses (10-22 µg/kg [4.5-10 µg/lb]) in two horses, then a final dosage of 22 µg/kg (10 µg/lb) was administered to six horses IV and SQ in a two-period randomized cross-over study performed over a 3-month study period. Blood samples were collected for measurement of plasma insulin and glucose concentrations during a 24-hr study period. Both IV and SQ somatostatin resulted in decreased insulin and increased glucose concentrations. SQ somatostatin resulted in a longer clinical effect, with return to baseline insulin occurring at 1.5 hr postadministration, versus 45 min for IV. Both IV and SQ administration of somatostatin to normal horses resulted in decreased insulin and increased glucose concentrations, likely due to suppression of insulin secretion by somatostatin. A more prolonged effect was seen following SQ administration as compared to IV administration, and no adverse effects were noted at varying doses. This study provides additional information regarding the effect of somatostatin administration on insulin and glucose concentrations in clinically healthy horses.

Relationship Between β-cell Response and Insulin Sensitivity in Horses based on the Oral Sugar Test and the Euglycemic Hyperinsulinemic Clamp

Background

A hyperbolic relationship between β‐cell response and insulin sensitivity (IS) has been described in several species including rodents, dogs, and humans. This relationship has not been elucidated in the horse.

Hypothesis/Objectives

To determine whether the hyperbolic relationship between β‐cell response and IS exists in horses by using indices of β‐cell response from the oral sugar test (OST) and IS measurements from the euglycemic hyperinsulinemic clamp (EHC). A second aim was to compare how well IS estimates from the OST and EHC correlate.

Animals

Forty‐nine horses with different degrees of insulin regulation (normal‐to‐severe insulin dysregulation).

Methods

Cross‐sectional study. Horses were examined with an OST and an EHC.

Results

Decreased IS was associated with increased β‐cell response in the horses. Nine of 12 comparisons between indices of β‐cell response and IS measures fulfilled the criteria for a hyperbolic relationship. Indices of IS calculated from the OST correlated highly with the insulin‐dependent glucose disposal rate (M) and the insulin‐dependent glucose disposal rate per unit of insulin (M/I) determined from the EHC (r = 0.81–0.87).

Conclusions and Clinical Importance

A hyperbolic relationship between β‐cell response and IS exists in horses, which suggest that horses with insulin dysregulation respond not only with postprandial hyperinsulinemia but are also insulin resistant. The OST is primarily a test for β‐cell response rather than a test for IS, but calculated indices of IS from the OST may be useful to estimate IS in horses, especially when the horse is insulin resistant.

Feeding practice and influence on selected blood parameters in show jumping horses competing in Switzerland

The aim of this study was to compare the nutritional management of show jumping horses in practice with recommendations from the literature. Additionally, the effects of these feeding practices on several blood metabolic parameters before and after exercise were studied. Blood samples were collected in the field from 27 different horses at 71 trials on the level M1 to S2 show jumping competitions in Switzerland and questionnaires on feeding practice of the studied horses were evaluated. The questionnaires revealed that during training and on tournament days horses received on average 3.1 kg of concentrate per day (min. 2.0 kg, max. 6.6 kg) divided into two to three meals. The horses were fed on average 6.9 kg of roughage per day (min. 4.0 kg, max. 13.0 kg). Additionally, it was observed that the horses received the last meal on average 6 h 10 min (min. 1 h 50 min, max. 12 h 30 min) before the start of the first show jumping turn, respectively, 7 h 30 min (min 1 h 50 min, max. 13 h 0 min) before the second turn. Seven horses (35%) had access to hay waiting in the trailer between two turns. The statistical analysis revealed no significant influence of the concentrate feeding time point on lactate, triglyceride and insulin levels, but a significant influence on free fatty acids (FFA) and blood glucose concentrations. Roughage feeding of the show jumping horses 2-4 h prior to exercise revealed the most remarkable changes in blood parameters during the show jumping course. These results received under field conditions should be approved in future under standardized conditions.