estradiol-3-benzoate and Hypoglycemia

Steroid positive-feedback activation of the gonadotropin-releasing hormone (GnRH)-pituitary luteinizing hormone (LH) neuroendocrine axis propagates the pre ovulatory LH surge, a crucial component of female reproduction. Our work shows that this key event is restrained by inhibitory metabolic input from hindbrain A2 noradrenergic neurons. GnRH neurons express the ultra-sensitive energy sensor adenosine 5'-monophosphate-activated protein kinase (AMPK); here, we investigated the hypothesis that GnRH nerve cell AMPK and peptide neurotransmitter responses to insulin-induced hypoglycemia are controlled by hindbrain lack of the oxidizable glycolytic end-product L-lactate. Data show that hypoglycemic inhibition of LH release in steroid-primed ovariectomized female rats was reversed by coincident caudal hindbrain lactate infusion. Western blot analyses of laser-microdissected A2 neurons demonstrate hypoglycemic augmentation [Fos, estrogen receptor-beta (ER-β), phosphoAMPK (pAMPK)] and inhibition (dopamine-beta-hydroxylase, GLUT3, MCT2) of protein expression in these cells, responses that were normalized by insulin plus lactate treatment. Hypoglycemia diminished rostral preoptic GnRH nerve cell GnRH-I protein and pAMPK content; the former, but not the latter response was reversed by lactate. Results implicate caudal hindbrain lactoprivic signaling in hypoglycemia-induced suppression of the LH surge, demonstrating that lactate repletion of that site reverses decrements in A2 catecholamine biosynthetic enzyme and GnRH neuropeptide precursor protein expression. Lack of effect of lactate on hypoglycemic patterns of GnRH AMPK activity suggests that this sensor is uninvolved in metabolic-inhibition of positive-feedback-stimulated hypophysiotropic signaling to pituitary gonadotropes.

Topics: Adrenergic Neurons; AMP-Activated Protein Kinases; Animals; Blood Glucose; Drug Administration Routes; Drug Administration Schedule; Estradiol; Female; Gene Expression Regulation; Gonadotropin-Releasing Hormone; Hypoglycemia; Insulin; Lactic Acid; Luteinizing Hormone; Neuropeptides; Ovariectomy; Preoptic Area; Proto-Oncogene Proteins c-fos; Rats; Rats, Sprague-Dawley; Rhombencephalon

Insulin and corticosterone signal energy surfeit and deficiency, respectively, to metabolic structures in the brain, including the hypothalamic arcuate nucleus (ARH). This peripheral input may be subject to ovarian control, since ovariectomy (OVX) increases insulin receptor transcripts and decreases glucocorticoid receptor protein in the hypothalamus. The present studies examined the hypothesis that estradiol regulates basal and hypoglycemic patterns of ARH insulin and glucocorticoid receptor mRNA expression, and governs habituation of these gene profiles to recurring intermediate insulin administration. The premise that estrogen receptor-alpha (ERalpha) and beta (ERbeta) gene profiles may be regulated differentially during acute and chronic hypoglycemia in the presence of estradiol was also evaluated. Insulin receptor-beta chain (InsRb), type-II glucocorticoid receptor (GR), ERalpha, and ERbeta mRNA levels in ARH tissue microdissected from estradiol benzoate (EB)- and oil-implanted OVX rats after single or serial sc neutral protamine Hagedorn insulin (NPH) injection were measured by quantitative real-time RT-PCR. ARH InsRb gene profiles were decreased, relative to baseline, after either one or four NPH injections in OVX + EB rats; mean mRNA levels were significantly lower after serial dosing since basal InsRb transcripts were diminished by precedent NPH treatment. InsRb transcription rates did not differ among OVX + oil treatment groups. Acute insulin elevated ARH GR mRNA relative to baseline in both EB- and oil-implanted rats. Prior NPH injections increased basal GR gene expression and suppressed transcriptional reactivity to a fourth dose of NPH in OVX + EB, but not OVX + oil animals. ARH ERalpha and ERbeta mRNA levels were increased or decreased, respectively, after one insulin dose in OVX + EB rats. Baseline expression of these genes was correspondingly augmented or suppressed after precedent NPH treatment, but ERalpha and ERbeta transcripts were not modified relative to these adjusted baselines after a fourth NPH dose. In the presence of estradiol, ARH InsRb and GR gene profiles exhibit divergent modifications during acute NPH-induced hypoglycemia, as well as opposite adjustments in baseline expression after serial NPH dosing. GR transcriptional acclimation to recurring NPH administration was also estrogen-dependent. Further research is needed to characterize potential effects of adjustments in ARH neuronal sensitivity to insulin and corticosterone

Topics: Animals; Arcuate Nucleus of Hypothalamus; Estradiol; Estrogen Receptor alpha; Estrogen Receptor beta; Female; Gene Expression Profiling; Hypoglycemia; Hypoglycemic Agents; Insulin, Isophane; Ovariectomy; Rats; Rats, Sprague-Dawley; Receptor, Insulin; Receptors, Glucocorticoid; RNA, Messenger

Oestradiol regulates basal food intake and glucagon and corticosterone secretion, but its influence on these responses to acute and recurring hypoglycaemia remains unclear. The present study utilised an experimental model for repeated intermediate-acting insulin-induced hypoglycaemia that replicates the route of delivery, frequency of administration, and duration of insulin action in the clinical setting. Groups of ovariectomised (OVX) rats were implanted with s.c. capsules containing oestradiol benzoate (EB) or oil, and injected with one or four doses of Humulin neutral protamine Hagedorn (HN), on as many days, or diluent alone. Baseline feeding followed divergent trends in EB- versus oil-implanted animals over a 9-h period after final injections. Recurring HN-induced hypoglycaemia resulted in significantly greater baseline-corrected food intake in OVX + EB and OVX + oil groups, relative to acute hypoglycaemic hyperphagia. Although oestradiol did not modify net food consumption after single or serial HN doses, EB replacement maintained uniform feeding over time in each treatment paradigm. Baseline glucagon and corticosterone secretion was higher in EB- versus oil-treated OVX rats. Oestradiol prolonged acute hypoglycaemic glucagonemia, and increased the magnitude, but shortened the duration, of glucagon secretion during recurring hypoglycaemia. OVX + oil rats responded to both acute and recurring hypoglycaemia with elevated corticosterone secretion at a single time point, which was advanced from +6 to +4 h during recurrent insulin-induced hypoglycemia, whereas OVX + EB animals exhibited increased plasma hormone levels at both +4 and +6 h in response to each paradigm. Area-under-the curve analyses showed that total glucagon and corticosterone release was greater in EB- versus oil-implanted rats after both single and serial dosing with HN. These results demonstrate that repeated HN administration increases food intake in female rats via oestrogen-independent mechanisms, but that oestradiol preserves temporal patterns of hypoglycaemic hyperphagia. The data also reveal that normo- and hypoglyacemic glucagon and corticosterone secretion are enhanced in the presence of oestrogen. Further studies are necessary to identify the sites and cellular substrates that are responsible for this hormonal regulation of behavioural and endocrine responses to prolonged hypoglycaemia.

Topics: Animals; Area Under Curve; Blood Glucose; Eating; Estradiol; Female; Humans; Hypoglycemia; Hypoglycemic Agents; Insulin; Male; Ovariectomy; Rats; Rats, Sprague-Dawley

The ovarian steroid hormone, estradiol, is one of several peripheral metabolic signal modulators that are integrated at the level of the arcuate nucleus of the hypothalamus (ARH), and is implicated in the control of ARH neuropeptides that maintain energy balance, including neuropeptide Y (NPY) and proopiomelanocortin (POMC). The present studies utilized quantitative real-time RT-PCR techniques to examine the hypothesis that estradiol regulates ARH NPY, POMC, and cocaine- and amphetamine-related transcript (CART) gene expression during acute insulin-induced hypoglycemia (IIH) and that adaptive modifications in transcriptional reactivity during recurring exposure are steroid dependent. ARH tissue was obtained by micropunch dissection from estradiol benzoate- and oil-implanted ovariectomized (OVX) rats that were treated by subcutaneous injection of one or four doses of the intermediate insulin formulation, Humulin NPH, over as many days, or vehicle alone. Our data show that in OVX plus estradiol benzoate and OVX plus oil groups, a single injection of insulin did not modify gene expression profiles, with the exception of acute hypoglycemic reduction of ARH NPY transcripts in the presence of estrogen. Prior exposure to daily hypoglycemia significantly diminished basal NPY and POMC mRNA levels in estradiol benzoate-, but not oil-implanted OVX rats, but elevated baseline CART transcripts in oil-treated animals. Recurring IIH enhanced ARH NPY gene expression relative to baseline, irrespective of the estradiol manipulation, but net tissue levels were greater in the absence of estrogen. In contrast, reexposure to hypoglycemia decreased POMC and CART gene transcription in estradiol benzoate- and oil-implanted OVX animals, respectively, relative to the single-dose groups. These studies show that estrogen modulates the impact of precedent exposure to IIH on basal and/or hypoglycemia-associated patterns of expression of ARH neuropeptide genes of characterized significance for energy homeostasis. The novel evidence for transcriptional acclimation of NPY, POMC, and CART to recurring IIH supports the possibility that adaptation of compensatory behavioral and physiological responses to acute versus chronic exposure to this metabolic stress may reflect neural regulatory mechanisms involving one or more neurotransmitters encoded by these genes.

Topics: Animals; Arcuate Nucleus of Hypothalamus; Estradiol; Female; Gene Expression Regulation; Hypoglycemia; Insulin; Nerve Tissue Proteins; Neuropeptide Y; Ovariectomy; Pro-Opiomelanocortin; Rats; Rats, Sprague-Dawley; Transcription, Genetic