Summary
The existence of large amounts of insulin in rat brain and of a porcine- or rat-like
insulin in guinea pig brain have been disputed on the basis of differing results from
standard (Method I) and hydrophobic adsorption techniques (Method II) for concentrating
insulin from acid ethanol extracts. To try to resolve these differences, acid ethanol
extracts of rat and guinea pig brains were divided into equal aliquots and concentrated
for insulin radioimmunoassay (RIA) by both techniques. The RIA used guinea pig anti-porcine
insulin serum, with 50% B0 for purified pancreatic porcine, rat and guinea pig insulin standards being 1.35,
2.38 and > 1,000 ng/ml, respectively. Oral glucose (4 g/kg) produced plasma glucose
of 377 mg/dl in a guinea pig by 20 min but was not associated with any porcine- or
rat-like immunoreactive insulin. Dilutions of guinea pig and rat brain extracts had
parallel cross-reactivity with insulin standard curves. Insulin contents of rat brain
(uncorrected for recovery) against porcine and rat insulin standards, respectively,
were 1.33 and 1.93 ng/g (Method I) and 5.93 and 11.67 ng/g (Method II). Rat plasma
was 0.85 and 1.42 ng/ml, respectively. Guinea pig contained 1.35 and 1.89 ng/g (uncorrected),
respectively (Method I), and 2.99 and 5.62 ng/g, respectively (Method II). Guinea
pig plasma was below the sensitivity of the RIA (< 0.15 ng/ml). These results suggest
that a porcine- or rat-like insulin may exist in guinea pig brain.
Key-Words:
Non-Pancreatic Insulin Immunoreactivity
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Guinea Pig Brain
