Sex-associated differences in pancreatic β cell function in healthy preweaning pony foals

Pancreatic β cells are responsive to a range of stimuli during early post natal life in healthy pony foals. However, little is known about whether these responses are sex-linked.

To determine pancreatic β cell responses to the insulin secretagogues, glucose, arginine and tolbutamide, in fillies and colts during the first 3 months after birth.

In vivo experiment examining sex differences in pancreatic β cell function in foals.

Female (n = 8) and male (n = 5) pony foals were infused i.v. with glucose (0.5 g/kg bwt 40% dextrose), arginine (100 mg/kg bwt) or tolbutamide (10 or 20 mg/kg bwt) over 5 min, at 48 h intervals, to assess pancreatic β cell function at ages 2 and 12 weeks. Blood samples (4 ml) were taken through a jugular catheter at -30, -15 and 0 min (immediately before) and 5, 15, 30, 45, 60, 90 and 120 min after glucose, arginine and tolbutamide administration for measurements of plasma glucose, α-amino-nitrogen and insulin concentrations.

The maximum increment in plasma insulin concentration in response to glucose was significantly higher in female (395 ± 58 ng/l) than male (172 ± 37 ng/l, P<0.05) pony foals 2 weeks after birth and the area under the insulin curve was significantly greater in females at this age. At 12 weeks, the insulin increment in response to glucose was significantly greater in fillies 45 min post infusion. The β cell responses to arginine and tolbutamide were not sex-linked at either age.

These data show that in ponies, fillies have a greater β cell response to glucose than colts in early post natal life. Since glucose clearance was unaffected by sex, the results suggest that fillies may be less insulin sensitive than colts shortly after birth. Innate sex differences in the secretion and action of insulin in early post natal life may influence tissue development and growth with potentially more long-term metabolic consequences.