Ghrelin does not impact the blunted counterregulatory response to recurrent hypoglycemia in mice

Abstract

IntroductionRecurrent episodes of insulin-induced hypoglycemia in patients with diabetes mellitus can result in hypoglycemia-associated autonomic failure (HAAF), which is characterized by a compromised response to hypoglycemia by counterregulatory hormones (counterregulatory response; CRR) and hypoglycemia unawareness. HAAF is a leading cause of morbidity in diabetes and often hinders optimal regulation of blood glucose levels. Yet, the molecular pathways underlying HAAF remain incompletely described. We previously reported that in mice, ghrelin is permissive for the usual CRR to insulin-induced hypoglycemia. Here, we tested the hypothesis that attenuated release of ghrelin both results from HAAF and contributes to HAAF.MethodsC57BL/6N mice, ghrelin-knockout (KO) + control mice, and GhIRKO (ghrelin cell-selective insulin receptor knockout) + control mice were randomized to one of three treatment groups: a “Euglycemia” group was injected with saline and remained euglycemic; a 1X hypoglycemia (“1X Hypo”) group underwent a single episode of insulin-induced hypoglycemia; a recurrent hypoglycemia (“Recurrent Hypo”) group underwent repeated episodes of insulin-induced hypoglycemia over five successive days.ResultsRecurrent hypoglycemia exaggerated the reduction in blood glucose (by ~30%) and attenuated the elevations in plasma levels of the CRR hormones glucagon (by 64.5%) and epinephrine (by 52.9%) in C57BL/6N mice compared to a single hypoglycemic episode. Yet, plasma ghrelin was equivalently reduced in “1X Hypo” and “Recurrent Hypo” C57BL/6N mice. Ghrelin-KO mice exhibited neither exaggerated hypoglycemia in response to recurrent hypoglycemia, nor any additional attenuation in CRR hormone levels compared to wild-type littermates. Also, in response to recurrent hypoglycemia, GhIRKO mice exhibited nearly identical blood glucose and plasma CRR hormone levels as littermates with intact insulin receptor expression (floxed-IR mice), despite higher plasma ghrelin in GhIRKO mice.ConclusionsThese data suggest that the usual reduction of plasma ghrelin due to insulin-induced hypoglycemia is unaltered by recurrent hypoglycemia and that ghrelin does not impact blood glucose or the blunted CRR hormone responses during recurrent hypoglycemia.

Role of the Adrenal Medulla in Hypoglycaemia-Associated Autonomic Failure—A Diabetic Perspective

“…Indeed, in the same study, the authors investigated the potential role of ghrelin in HAAF using ghrelin knockout mice and ghrelin cell-selective insulin receptor knockout mice and found that the counterregulatory responses (plasma glucagon and adrenaline) were reduced in both strains similar to the C57Bl/6N mice after recurrent hypoglycaemia. In a similar fashion, plasma ghrelin was also blunted in both the single and recurrent insulin injection groups [89]. The authors concluded that ghrelin deletion or elevation did not affect blood glucose or counterregulatory hormone responses, suggesting that ghrelin does not play a role in HAAF [89].…”

“…In a similar fashion, plasma ghrelin was also blunted in both the single and recurrent insulin injection groups [89]. The authors concluded that ghrelin deletion or elevation did not affect blood glucose or counterregulatory hormone responses, suggesting that ghrelin does not play a role in HAAF [89].…”

“…In a validated mouse model of HAAF, C57Bl/6N mice were subjected to three protocols: saline injection, a single insulin injection, or five recurrent days of insulin injections [89]. The authors found that recurrent insulin injections lowered blood glucose and blunted glucagon and adrenaline responses [89].…”

“…In a validated mouse model of HAAF, C57Bl/6N mice were subjected to three protocols: saline injection, a single insulin injection, or five recurrent days of insulin injections [89]. The authors found that recurrent insulin injections lowered blood glucose and blunted glucagon and adrenaline responses [89]. To our knowledge this is the first study in mice that could successfully reproduce both components of the counterregulatory failure in response to recurrent hypoglycaemia.…”

“…All the above-mentioned results suggest that catecholamine synthesis is unlikely to be affected by recurrent hypoglycaemia. ↓ adrenaline response [89] 30 min from the last injection [89] ~16/7 ng/mL [89] Non-diabetic rats Insulin, 2 U/kg; i.p. [37] Twice a day for 3 days [37] ↓ expression of genes of proteins associated with exocytosis [37] 60 min from the last injection [37] Did not measure [37] Insulin, 5 U/kg; i.p.…”