I’m looking into reducing the refractory period through prolactin manipulation.

Here is one study with some suggestions: (LINK)

J Endocrinol. 2003 Dec;179(3):357-65.

Effects of acute prolactin manipulation on sexual drive and function in males.

Krüger TH, et al. Source
Department of Medical Psychology, University of Essen, Hufelandstrasse 55, 45122 Essen, Germany. tillmann.krueger@web.de

Abstract

The neuroendocrine response to sexual activity in humans is characterized by a pronounced orgasm-dependent increase of plasma levels of prolactin. In contrast to the well-known inhibitory effects of chronic hyperprolactinemia on sexual drive and function, the impact of acute prolactin alterations on human sexual physiology is unknown. Therefore, this study was designed to investigate the effects of acute manipulation of plasma prolactin on sexual behavior. Ten healthy males participated in a single-blind, placebo-controlled, balanced cross-over design. Prolactin levels were pharmacologically increased to high levels (protirelin, 50 micro g i.v.) or reduced to low physiological concentrations (cabergoline, 0.5 mg p.o.). Sexual arousal and orgasm were then induced by an erotic film and masturbation. In addition to continuous neuroendocrine and cardiovascular recordings, the quality and intensity of the acute sexual drive, arousal, orgasm and refractory period were assessed by extensive psychometric measures. Administration of cabergoline decreased prolactin levels and significantly enhanced all parameters of sexual drive.