GHRP-6 is a synthetic peptide that is designed to stimulate the release of hormone in animals, for experimental purposes. This chemical is very similar go GHRH but it acts on different receptors in the body once administered.
This chemical was designed to mimic the effects of the natural hormone ghrelin. GHRP-6 can also be administered alongside insulin, though this is simply designed to enhance the effects of the chemical so GHRP-6 can be used, to better monitor eating and metabolism effects.
Regulating GHRP-6 in GH Secretions
Naturally, GHRP-6 is used to release hormone in an animal which may be related to the endogenous compound of the chemical’s structure.
In vivo hormone responses to GHRP-6 were investigated in pentobarbital anesthetized rats as a way of learning to avoid influencing endogenous somatostatin or GHRH secretions that were seen in a historical assessment.
Hypophsectoyzed-transplanted rats that had two hypophyses underneath their renal capsules were used for this experiment, though follow up work used rats that were pre-treated with GHRH.
Results indicate that rats that were pretreated with GHRH showed an increase in hormone response, compared to those that were exposed to a saline placebo.
These effects were compared to the effects of GHRP-6, which were self-potentiating. The influence of estrogen, free fatty acids, glucocorticoids and bombesin on the responsive nature of GHRP-6 was also compared in rats that remained intact.
In this experiment the rats exposed to GHRP-6 were given a surgical ablation of their hypothalamus 36 hours before applications of these chemicals would begin, to ensure that the hormone response delivered was directly related to experimental intervention.
A similar response was seen between animals that were administered GHRP-6 and those that were pretreated with GHRH throughout the two week experiment. Both rats treated with testosterone and estrogen were seen to have a larger hormone response when exposed to GHRP-6, compared to those that were left untreated.
However, chronic dexa-methasone administration caused an acute raise in circulating FFA levels while applying bombesin to the rats severely inhibited the hormone. hormone levels decreased when dexamethasone was applied, while this did not affect hormone levels when the rats were pre-treated with GHRH.
Sex Difference in Hormone Release
Hormone secretions were measured in both conscious and unconscious female rats after the administration of GHRP-6, to better determine how these effects changed between the sexes.
In females the hormone in the plasma was elevated significantly when compared to the levels in the males. These effects began to take shape around 15 minutes after the injection was administered.
Males that were provided GHRP-6 saw a suppression of the episodic hormone secretions along with desensitization once the second GHRP-6 injection was administered 6 hours later. By contrast, females saw a similar hormone secretion after both injections.
After two weeks of GHRP-6 injections twice per day, plasma hormone concentrations in males decreased while female rats saw an increase that was consistent across their dosage.
The desensitization to GHRP-6 injections that was seen in the male rats that were conscious for the experiment was not seen in a group of pretobarbital anesthetized rats that was exposed to the same applications of the peptide. This suggests that GHRP-6 injections are enhanced by the presence of somatostain releases that occur when an animal is conscious.
Once the 14 days of study were completed, the average concentration of hormone in females was lower than that of male rats. There was also a lower pituitary hormone concentration in females while higher secretions were seen after GHRP-6 was administered.