OBJECTIVE: The recently isolated endogenous GH secretagogue, named ghrelin, is a gastric peptide of 28 amino acids with an n-octanoylation in the serine 3 that confers the biological activity to this factor. Ghrelin has been shown to directly stimulate GH release in vivo and in vitro and to be involved in the regulation of gastric acid secretion and motility. In the present work we have studied gender and gonadal dependency of ghrelin mRNA expression in rat stomach. DESIGN AND METHODS: We analysed ghrelin mRNA expression in rat stomach by Northern blot analysis. We also examined the effect of gonadal steroid deprivation on ghrelin mRNA expression. RESULTS AND CONCLUSIONS: The results obtained showed clearly that ghrelin gastric mRNA expression increased with age in young rats (up to 90 days old) but exhibited no significant sex difference at each age tested. Ghrelin mRNA levels were lowest at postnatal day 9, reaching a stable level of expression at day 40 in both female and male rats, although the increase in female rats appears much more gradual than that in males. Moreover, neither ovariectomy nor orchidectomy significantly modified ghrelin mRNA gastric levels in adult rats. In conclusion, these data indicate that ghrelin mRNA expression is associated with age and that a progressive increase is present from the perinatal period up to a stable level after puberty. Gonadal hormones did not alter ghrelin mRNA levels. Taken together, these data showed that ghrelin mRNA levels in young rats are age but not gender dependent, and are not influenced by gonadal steroids.
O Gualillo, JE Caminos, M Kojima, K Kangawa, E Arvat, E Ghigo, FF Casanueva and C Dieguez
R Peino, V Pineiro, O Gualillo, C Menendez, J Brenlla, X Casabiell, C Dieguez and FF Casanueva
OBJECTIVE: Leptin secretion is reduced by low temperatures in experimental animals, and this effect has been explained as an adaptive mechanism to cold environments. This study investigated the in vitro effects of cold exposure on human white adipose tissue. DESIGN: To understand whether the low temperature action is a direct or a mediated effect, leptin secretion was assessed in vitro in human omental adipose tissue incubated at varied temperatures, from 38 donors. As an internal control, the effect of reduced temperatures on in vitro GH secretion by GH3 cells was assessed. METHODS: Measurement of hormones secretion was carried out with an RIA, while human ob gene mRNA expression was assessed with reverse transcription PCR. RESULTS: Compared with the standard temperature of 37 degrees C, leptin secretion by human adipose tissue was significantly (P<0.05) reduced when the incubations were carried out at 34.5 degrees C (41% inhibition), and 32 degrees C (68% inhibition), with no parallel changes in the ob mRNA expression. At these reduced temperatures, glucocorticoid-mediated leptin secretion was well preserved. When the effect of reduced temperatures was assessed on in vitro GH secretion, a superimposable reduction was observed. CONCLUSIONS: These results indicate: (i) that low temperatures reduce leptin secretion by acting directly on the adipose tissue and (ii) that the similar reduction in a hormone unrelated to energy metabolism, such as GH, suggests that the observed reduction is a mechanical perturbation of leptin secretion, which may be devoid of physiological implications.