The analysis of exogenous ghrelin plasma activity and tissue distribution.

OBJECTIVES: Ghrelin presents a multiplicity of biological functions, what is consistent with widespread expression of this peptide and its receptors. Ghrelin may act locally, but it may also influence distant cells. The aim of the study was to assess plasma activity of exogenous ghrelin and its distribution in rats.

DESIGN: Plasma radioactivity of (125)I-ghrelin (cpm) was analyzed in blood specimens collected after (125)I-ghrelin administration. Tissue uptake of (125)I-ghrelin (cpm/mg) was evaluated in 27 tissues obtained during an autopsy performed 1, 2 and four hours after (125)I-ghrelin administration. The radioactivity of the tissue specimen (cpm) was divided by the weight of the specimen (mg).

RESULTS: Plasma (125)I-ghrelin radioactivity decreased rapidly after peptide administration. The half-life time of (125)I-ghrelin was 15-18 minutes. The analysis of (125)I-ghrelin distribution revealed three profiles of its tissue uptake. The first profile was characterized by decreasing radioactivity (e.g. brain, kidney, liver). Increasing tissue radioactivity followed by a gradual decrease (second profile) was observed for example in stomach, intestine and thyroid. The third profile was described as a relatively stable radioactivity (e.g. lung, myocardium). Despite of Lugol's solution administration, thyroid uptake of (125)I-ghrelin was notably higher than in other tissues (second and third profile).

CONCLUSIONS: Exogenous ghrelin uptake in tissues that produce this peptide suggests, that ghrelin influences the biology and function of these cells also in endocrine way. Similarly, the accumulation of peptide observed in the third profile (e.g. thyroid) may reflect a potential role of ghrelin in these organs.