Liver-derived IGF-I regulates GH secretion at the pituitary level in mice.

• We have reported that liver-specific deletion of IGF-I in mice (LI-IGF-I-/-) results in decreased circulating IGF-I and increased GH levels. In the present study, we determined how elimination of hepatic IGF-I modifies the hypothalamic-pituitary GH axis to enhance GH secretion. The pituitary mRNA levels of GH releasing factor (GHRF) receptor and GH secretagogue (GHS) receptor were increased in LI-IGF-I-/- mice, and in line with this, their GH response to ip injections of GHRF and GHS was increased. Expression of mRNA for pituitary somatostatin receptors, hypothalamic GHRF, somatostatin, and neuropeptide Y was not altered in LI-IGF-I-/- mice, whereas hypothalamic IGF-I expression was increased. Changes in hepatic expression of major urinary protein and the PRL receptor in male LI-IGF-I-/- mice indicated an altered GH release pattern most consistent with enhanced GH trough levels. Liver weight was enhanced in LI-IGF-I-/- mice of both genders. In conclusion, loss of liver-derived IGF-I enhances GH release by increasing expression of pituitary GHRF and GHS receptors. The enhanced GH release in turn affects several liver parameters, in line with the existence of a pituitary-liver axis.

Nyckelord

Animals

Female

Growth Hormone

blood

genetics

secretion

Growth Hormone-Releasing Hormone

pharmacology

Hypothalamus

metabolism

Insulin-Like Growth Factor I

analysis

genetics

physiology

Liver

anatomy & histology

metabolism

Male

Mice

Mice

Knockout

genetics

Neuropeptides

physiology

Organ Size

Pituitary Gland

secretion

Proteins

genetics

RNA

Messenger

metabolism

Receptors

Cell Surface

physiology

Receptors

Prolactin

genetics

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