Large or small doses of synthetic LH-RH were injected into the carotid artery or intramuscularly in three anestrous ewes and one vasectomized ram. Intracarotid injection of 5 pg of synthetic LH-RH elicited monophasic responses in LH-release; the highest levels of serum LH were reached within 5-10 min after injection of LH-RH, followed by a gradual decrease. Injection of 250 pg of LH-RH resulted in a rise of serum LH within 5-10 min which was indistinguishable in magnitude from that after 5 pg of LH-RH. These levels remained steady or kept rising very gradually for 25 rnin or longer, then again started rising sharply. The peak levels were observed at 1.5 hr after injection, followed by a gradual decrease. Four hours after injection of LH-RH, serum LH levels were still higher than during the preinjection levels. Intramuscular injection of a large dose of LH-RH elicited patterns similar to those observed following intracarotid injection of LH-RH. The magnitude of response after intramuscular injection was the same or greater than that induced by the intracarotid injection of the same dose of LH-RH.
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Arimura et al. (1972) studied this question.