Glucoreceptors located inside the blood-brain barrier mediate hypoglycemia-induced LH inhibition in man.
OBJECTIVE
To establish the role of hyperinsulinemia and hypoglycemia during the insulin tolerance test (ITT) in the regulation of luteinizing hormone (LH) secretion and the location with respect to the blood-brain barrier (BBB) of the glucosensitive areas controlling LH release.


METHODS
The LH-secretory pattern during an ITT (0.15 IU/kg body weight) was evaluated in 8 normal men during infusion with normal saline (control test), glucose or fructose.


RESULTS
lnsulin-induced hypoglycemia produced a significant decrement in serum LH levels in the control test, but not when the concomitant infusion of glucose prevented hypoglycemia. Fructose infusion did not change LH decrease during ITT.


CONCLUSIONS
These data exclude a direct role of hyperinsulinemia in the mechanism underlying the inhibition of LH secretion during ITT. Furthermore, since glucose but not fructose crosses the BBB, the LH decrease during ITT appears to be generated by hypoglycemia at the level of glucosensitive areas located inside the BBB.
Coiro
Vittorio
V
Department of Internal Medicine and Biomedical Sciences, University of Parma, Parma, Italy. vittorio.coiro@unipr.it
Volpi
Riccardo
R
Capretti
Luigi
L
Manfredi
Guido
G
Galli
Paola
P
Saccani-Jotti
Gloria
G
Chiodera
Paolo
P
D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D001812:Blood-Brain Barrier / Q000378:metabolism*; D005632:Fructose / Q000008:administration & dosage / Q000097:blood; D006801:Humans; D006946:Hyperinsulinism / Q000097:blood / Q000378:metabolism*; D007003:Hypoglycemia / Q000097:blood / Q000378:metabolism*; D007004:Hypoglycemic Agents; D007275:Injections, Intravenous; D007328:Insulin / Q000008:administration & dosage / Q000097:blood; D007986:Luteinizing Hormone / Q000037:antagonists & inhibitors* / Q000097:blood; D008297:Male; D009994:Osmolar Concentration; D011956:Receptors, Cell Surface / Q000378:metabolism*
D001786:Blood Glucose; D007004:Hypoglycemic Agents; D007328:Insulin; D011956:Receptors, Cell Surface; C027786:glucose receptor; D005632:Fructose; D007986:Luteinizing Hormone