Details

Autor(en) / Beteiligte

• DePaolo, L V
• Barraclough, C A

Titel

Dose Dependent Effects of Progesterone on the Facilitation and Inhibition of Spontaneous Gonadotropin Surges in Estrogen Treated Ovariectomized Rats

Ist Teil von

• Biology of reproduction, 1979-11, Vol.21 (4), p.1015-1023

Ort / Verlag

United States: Society for the Study of Reproduction

Erscheinungsjahr

1979

Quelle

MEDLINE

Beschreibungen/Notizen

• These studies determined whether fluctuating physiological plasma progesterone (P) concentrations facilitate as well as inhibit spontaneous LH and FSH surges in E 2 primed, ovariectomized (OVX) rats. Two weeks after ovariectomy (Day 0), Silastic implants of estradiol-17β (E 2 ) were inserted s.c. at 0900 h into all animals. Silastic P implants of various lengths, which produced plasma P levels ranging between 5-20 ng/ml, were implanted s.c. into separate groups of E 2 treated OVX rats 72 h later (Day 3). Another group of E 2 treated rats received a s.c. injection of 2 mg P on Day 3. As plasma P levels increased, greater peak plasma LU and FSH levels were achieved during the afternoon of Day 3. However, higher concentrations of plasma P were required to affect significantly spontaneous FSH than LH surges. Further, as plasma levels of P increased, the onset of release of both gonadotropins occurred earlier in the afternoon of Day 3. When plasma P levels were increased above 17 ng/ml, further facilitation of either gonadotropin surge was not observed. Regardless of the plasma P levels present on Day 3, this steroid did not inhibit spontaneous LH surges on this day. In contrast, the absence of spontaneous gonadotropin surges on Day 4 was related to P concentrations present in plasma on Days 3 and 4. In a separate experiment, the pituitary LH responses to 2 i.v. pulse injections of LHRH spaced 120 min apart were evaluated in 2 week OVX animals given E 2 , E 2 P or no steroid pretreatment. Both steroid treated groups released more LH than did nonsteroid treated animals in response to either LHRH injection. As well, pituitary LH responses to LHRH in E 2 and E 2 P treated rats were greater after the second than after the first injection. However, P treatment of E 2 primed animals tended to enhance the self-priming action of LHRH. These data demonstrate that: 1) low physiological P levels can facilitate spontaneous LH and FSH surges on Day 3 as well as inhibit these discharges on Day 4 in E 2 primed animals; 2) these P-induced responses are dose dependent; and 3) the facilitory action of P is exerted on CNS neurons and possibly on pituitary gonadotrophs.