Perfil de progesterona sérica em fêmeas bovinas utilizando implantes vaginais em diferentes situações fisiológicas

Abstract

Progesterone (P4) is an important steroid hormone in FTAI programs. Hormonal protocols used in FTAI programs involve considerable financial values, in which P4 represents 43% of the total cost. The P4 release process from vaginal implants occurs by passive diffusion, i.e., the drug release is driven by concentration gradient and enhanced by the contact area between the implant and vaginal epithelium. Given the importance of P4 in the protocols and the significance of this steroid in the treatment costs, several studies described the reutilization of P4 vaginal implants as an alternative to make this technology feasible. However, the results are controversial and the pattern of P4 releasing from vaginal implants used in cows with different luteal activity (amount of endogenous P4 synthesis) is not yet described. The aim of the present study was to evaluate the P4 profile in cows with different luteal activity treated with a new vaginal implant (1g of P4) for 8 days; evaluate and compare to each other and to a new vaginal implant the P4 releasing from implant previously used in females with different endogenous progesterone conditions; and correlate progesterone releasing from new and used (second use) implants with follicular dynamics. For this purpose, two experiments were performed. Experiment 1: Group 1(G1a) with corpus luteum during all treatment period; Group 2 (G2a) with corpus luteum during half of treatment period; Group 3 (G3a) without corpus luteum. At the beginning of treatment (D0), G1a and G2a animals had a functional corpus luteum which was formed eight days prior to implant insertion. Three day after implant insertion (D3), 0.15 mg of D-cloprostenol were administered in G2a animals. The G3a animals (n=10) started the treatment without ovarian luteal activity. Blood samples were collected on D0 in the morning and afternoon, D3, D5 and D8. P4 concentrations were determined by radioimmunoassay (RIA). Average P4 concentrations in each collection were compared by Tukey s test. G1a and G2a was different from G3a on D0 (5,3+3,1a; 5,3+1,4a and 0,6+0,3b ng/mL, respectively (p<0,05)) and on D3 (5,7+2,6a; 5,4+1,95a and 3,6+0,8b ng/mL, respectively (p<0,05)). On D5, 36 hours after PGF administration, P4 concentration of G2a became similar to G3a and both were different from G1a (G1a=3,3+1,6a, G2a=2,4+0,9b and G3a=2,1+0,7b ng/mL (p<0,05)). On D8, the groups maintained the same characteristics (G1a=3,1+1,3a, G2a=1,8+0,8b and G3a=1,6+0,6b ng/mL (p<0,05)). Furthermore, the difference in the P4 serum concentration between D3 and D0 were lower in G1a and G2a than in G3a (G1a=0,4+1,8a; G2=0,2+1,4a e G3=2,8+0,9b ng/mL (p<0,05)). In experiment 2, the same animals were reallocated into 4 groups without CL. Group 1(G1b) implants from G1a of Exp1; Group 2 (G2b) implants from G2a of Exp1; Group 3 (G3b) implants from G3a of Exp1; and Group 4 (G4b) new implants. There is no difference in the number of animals with P4 lower than 1 ng/mL (G1b = 16.7%, G2b = 66%, G3b = 50% and, G4b = 0; P=0,14) and in the number of times that this occurred in relation to the amount of samples evaluated (G1b = 12.5 %, G2b = 22.9 %, G3b = 12.5 % and, G4b = 0; P=0,07), i.e., there were no P4 releasing pattern from used implants and only new implants properly maintained the concentration of this hormone. The average follicular growth rate (G1b = 1,0+0,5; G2b = 1,0+0,3; G3b = 0,7+0,5 e G4b = 0,8+0,3) mm/day) and the diameter of the largest follicle on D8 (G1b = 13,0+3,3; G2b = 12,0+2,3; G3b = 10,5+2,9 e G4b = 11,4+0,6 mm) were also not affected by the releasing pattern of the implants. In conclusion, animals with CL and endogenous P4 during FTAI protocols consumed less P4 from the implants when compare to animals without CL; new P4 vaginal implants maintained adequate levels of P4 for TFAI, regardless the physiological condition of the treated animal; implants previously used by animals with different ovarian activity did not maintain the P4 profile similar to that observed with new implants; follicular dynamics was not changed by the lack of P4 releasing pattern from the used implants when compared to new implants; despite the greater progesterone release, did not affect follicular development pattern in heifers.