Exploring endocrine GH pattern in mice using rank plot analysis and random blood samples

Abstract

GH plays important pleiotropic roles in development, growth, metabolism, and aging of vertebrate species. Mouse mutants with altered GH signaling have been increasingly instrumental in studying somatotropic pathophysiology. However, the pulsatile characteristics of GH secretion are difficult to study in mice because catheterization is cumbersome and long-term serial sampling is limited by small body size and blood volume. We therefore developed an approach routinely applicable to mice, which detects endogenous, physiological GH pattern from randomly obtained spot samples. We determined individual hormone concentration in large groups of mice, ranked the data by magnitude, and statistically analyzed the resulting profiles. This revealed that the nadir-to-peak distribution of plasma GH concentration in mice was similar to other mammals, and that nycthemeral and sex differences existed as well. We found handling stress to be a potent immediate downregulator of circulating GH. We showed that samples need to be taken within seconds to reflect true endogenous levels, unaffected by stress. GH receptor/Janus kinase 2/signal transducer and activator of transcription 5 activation measured in the liver correlated strongly with plasma GH levels, but peak concentrations did not further increase the pathway activation. We applied this rank plot analysis to the GH-deficient and long-lived brain-specific IGF-1 receptor knockout (bIGF1RKO) mouse mutant and found a high proportion of low GH concentrations, indicative of extended trough periods and rare peaks. Taken together, we showed that rank plot analysis is a useful method that allows straightforward studies of circadian endogenous GH levels in mice.

Insulin-Like Growth Factor 1 Mediates Negative Feedback to Somatotroph GH Expression via POU1F1/CREB Binding Protein Interactions

“…Nonetheless, in the fasting state, the basal secretion of GH in S436A mice was significantly higher, which in the context of our studies represents an alteration in IGF-1 negative feedback. Our findings were further supported by utilizing the previously reported method of rank plot analysis to analyze the collected GH profiles (50). Using this method, we noted a trend to higher serum GH in S436A mice, fewer values in the nadir range, and more values in the intermediate range.…”

“…The evaluation of GH levels in mice is often difficult to perform given several limitations such as GH pulsatile release, limited blood volume from serial sampling, the short GH half-life, and the effects of stress, which rapidly reduce serum GH levels (46,50). Nonetheless, in the fasting state, the basal secretion of GH in S436A mice was significantly higher, which in the context of our studies represents an alteration in IGF-1 negative feedback.…”

Not So Giants: Mice Lacking Both Somatostatin and Cortistatin Have High GH Levels but Show No Changes in Growth Rate or IGF-1 Levels

“…ITT and GTT data were assessed by a two-way ANOVA followed by a Fisher's least significant differences post hoc test. Ranked plot analysis of GH was done by arranging GH values in order of magnitude as a rank plot, and the differences were compared by Wilcoxon signed-rank test, as previously reported (17). P Ͻ .05 was considered significant.…”

Dynamic, Sex-Differential STAT5 and BCL6 Binding to Sex-Biased, Growth Hormone-Regulated Genes in Adult Mouse Liver

“…In rats and mice, GH is secreted by the pituitary gland in a highly pulsatile manner in males, while in females GH secretion is more frequent, such that there is no prolonged GH-free interval between plasma hormone pulses (29,54,66). Ablation of circulating GH by hypophysectomy abolishes liver sex differences globally (61,62), and exogenous GH pulses restore male-biased gene expression (27,64).…”