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Influence of Testosterone on LHRH Release, LHRH mRNA and Proopiomelanocortin mRNA in Male Sheep 1
Author(s) -
Hileman Stanley M.,
Lubbers Laura S.,
Petersen Sandra L.,
Kuehl David E.,
Scott Christopher J.,
Jackson Gary L.
Publication year - 1996
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1111/j.1365-2826.1996.tb00831.x
Subject(s) - medicine , endocrinology , castration , proopiomelanocortin , cannula , testosterone (patch) , silastic , gonadotropin releasing hormone , pulsatile flow , biology , hypothalamus , hormone , luteinizing hormone , surgery
The mechanism whereby testosterone (T) reduces pulsatile LHRH and LH release is unknown. We tested the hypothesis that hypothalamic levels of LHRH mRNA decrease and proopiomelanocortin (POMC) mRNA increase coincident with reduced LHRH release induced by either long‐term or short‐term T treatment in male sheep. Experiment 1 examined the effect of long‐term T exposure on LHRH and LH release and LHRH and POMC mRNA levels. Yearling Suffolk rams were castrated and assigned to one of four treatments: 1) castrated (n = 4); 2) castrated, portal cannula (n = 5); 3) castrated +T (n = 4) and 4) castrated+T, portal cannula (n = 4). T‐treated males received ten 10‐cm silastic T‐implants immediately after castration. Surgical placement of devices for collecting hypophyseal‐portal blood occurred 2 to 3 months after castration. Seven to 10 days after surgery, blood samples were collected at 10‐min intervals for 8h from portal cannulated males or for 5 h from non‐cannulated males to assess pulsatile LHRH and/or LH release. Immediately after blood sample collection, hypothalamic tissue was collected for in situ measurement of LHRH or POMC mRNA. T‐treatment decreased ( P < 0.01) mean LHRH and LH and decreased ( P < 0.01) LHRH and LH pulse frequency. T did not significantly affect ( P > 0.10) silver grain area per LHRH neuron, but decreased ( P < 0.01) silver grain area per POMC neuron. Portal cannulation tended to decrease ( P = 0.057) silver grain area per LHRH neuron without significantly affecting ( P > 0.10) LHRH cell numbers while reducing ( P < 0.01) silver grain area per POMC neuron and POMC cell numbers. A second experiment examined the effect of 72 h of T‐infusion on LHRH and POMC mRNA levels. Castrated yearling males were assigned to receive either vehicle (n = 4) or T (768 ug/kg/day;n=4). Blood samples were collected at 10 min intervals for 4h prior to and during the final 4 h of infusion. Infusion of T decreased ( P < 0.01) mean LH and LH pulse frequency. T did not significantly affect ( P > 0.10) silver grain area per LHRH neuron or LHRH cell numbers. T reduced ( P < 0.01) silver grain area per POMC neuron without affecting ( P > 0.10) POMC cell number. We reject our hypothesis and conclude that reduced LHRH or heightened POMC gene expression are not mechanisms whereby T reduces pulsatile LHRH release in male sheep.