In rats, giving the GH‑releasing peptide sermorelin (GH‑RH 1‑29) by breathing it in (pulmonary inhalation) caused a strong rise in growth hormone, even more than a shot under the skin or a nasal spray, and the newer agmatine‑based version worked at much lower doses. This suggests inhalation could be a convenient way to boost GH, but the study is in animals, so human dosing and safety are still unknown.

Many studies have shown that human GH-RH(1-29)NH2 possesses full intrinsic activity of GH-RH(1-44)NH2 in vitro and in vivo. This investigation was performed to evaluate the efficacy of GH-RH(1-29)NH2 given by different routes of administration in stimulating GH release in rats. In each case GH-RH(1-29)NH2 was administered intravenously, subcutaneously, intranasally and by pulmonary inhalation at two different doses to groups of seven males rats. At a dose of 150 micrograms/kg GH-RH(1-29)NH2, the magnitude of GH response was significantly higher for the pulmonary inhalation group (355 +/- 33.2 ng GH/mL) than for the subcutaneous group (246 +/- 36 ng GH/mL) or for the intranasal group (175 +/- 30 ng GH/mL). The group injected intravenously with GH-RH(1-29)NH2 at a dose of 2.5 micrograms/kg showed the highest response, GH levels reaching 877.2 +/- 115 ng/mL. A similar pattern of responses was obtained for the superactive GH-RH(1-29) agmatine29 analog, MZ-3-149, at doses that were 50 times lower. Our results indicate a high bioavailability of GH-RH(1-29)NH2 or analog MZ-3-149 administered by a convenient pulmonary inhalation route. The GH-releasing effect of GH-RH(1-29)NH2 or analog MZ-3-149 delivered by pulmonary inhalation is superior to subcutaneous and intranasal administration.