Uptake, content, regulation of plasma concentrations, and binding of Tyr-MIF-1 by the adrenals

The known occurrence of opiates in the adrenals stimulated us to determine whether Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2), an endogenous peptide that can act as an antiopiate, is present in these glands and whether adrenalectomy affects its concentrations in plasma. The presence of Tyr-MIF-1 in the adrenals of the rat was shown by radioimmunoassay (RIA) and high performance liquid chromatography (HPLC). Binding sites for the tetrapeptide also were found in the adrenal. The concentrations and binding of Tyr-MIF-1 were higher in the adrenal medulla than in the adrenal cortex. The adrenals preferentially trapped 125I-Tyr-MIF-1 as compared with 99mTc-albumin after intravenous administration. However, after correction for tissue weight and vascular space, accumulation of 125I-Tyr-MIF-1 by the adrenals was in the general range seen for several other tissues. The concentrations of Tyr-MIF-1-like immunoreactivity determined by RIA in the plasma of adrenalectomized rats were increased in comparison with sham operated or unoperated controls. This approximate doubling was unchanged by the site of sampling: hepatic portal vein, renal vein, inferior vena cava, jugular vein, or truncal blood. Hypophysectomy, removal of the adrenal medulla, or treatment with corticosterone also did not block this increase. Tyr-MIF-1-like immunoreactivity in the plasma of adrenalectomized rats eluted at the same position by HPLC as did the synthetic Tyr-MIF-1 standard. Thus, the adrenal gland contains Tyr-MIF-1 and can affect its concentrations in plasma.