GENERAL

AND

COMPARATIVE

ENDOCRINOLOGY

78,299-302

(1990)

Radioimmunoassay of Ovarian Steroids in Plasmas of Ovulating Female Sea Bass (Dicentrarchus labrax) A. P. SCOTT,* A. V. M. CANARIO,?. AND F.

PFWTS

*Ministry of Agriculture, Fisheries and Food, Directorate of Fisheries Research, Fisheries Laboratory, Lowestoft, Suffolk, NR33 OHT, England; Wniversidade do Algarve, 8004 Faro, Portugal; and Slnstituto de Acuicultura de Torre de la Sal, Ribera de Cabanes (Castellon), Spain Accepted June 26, 1989 Radioimmunoassays of the free and conjugated fractions of plasmas from ovulating sea bass (Dicentrarchus labrax) have revealed the presence of several unusual polar steroids. Among them is 3a,17a,20~,21-tetrahydroxy-5~-pregnane.

At the time of oocyte final maturation in teleosts, the ovaries produce large amounts of C,, steroids, the structures of which appear to differ considerably between species. For example, the rainbow trout (Oncorhynchus mykiss) ovary synthesises mainly 17o,20@-dihydroxy-4-pregnen-3-one (17,20@P), the Atlantic croaker (Micropogonias undulatus) 17o1,20P,21-trihydroxy-4-pregnen-3-one (17,2Op,21-P), the dab (Limanda limundu) 17a,20o-dihydroxy-4-pregnen-3-one (17,20a-P) plus 3g,I701,20a-trihydroxy-5g-pregnane, and the plaice (Pleuronectes phtessu) 1l-deoxycortisol (17,21-P) plus 3a,17a,21-trihydroxy-5P-pregnan-20-one (3a,17,21-P-5g) (for complete references see Canario and Scott, 1990). Colombo et al. (1978) have investigated in vitro steroid production by the bass ovary. The major Czl steroid which they identified in postovulatory females was 17,21-P. However, their autoradiographs of thin-layer chromatography (TLC) plates showed that a large amount of radioactivity was associated with unidentified compounds with a very high polarity. There was no evidence for the presence of 17,2Og-P, the maturation-inducing steroid in salmonids. Prat et al. (1987) only found traces of the latter steroid in the blood of ovulating females.

We have developed radioimmunoassays (RIAs) for a wide range of Czi steroids, including 17,21-P. In the present study, we have applied them (plus testosterone and 17g-oestradiol assays) to the measurement of steroid levels in the free and conjugated fractions of plasmas obtained from six recently ovulated female bass (for a full description of methods see Canario and Scott, 1990). RESULTS

AND DISCUSSION

Table 1 shows the levels of immunoreactive material recorded in the various RI&. Figure 1 shows the patterns of steroid immunoreactivities on TLC. Only the conjugated fractions are shown, but the free fractions gave similar patterns. There were fairly high levels of 17,21-P immunoreactivity in the free and conjugated fractions of the plasmas. On TLC, however, there was no immunoreactivity in the position of the standard. There were two peaks, however, which exactly matched the elution positions of cortisol and cortisone. Although these steroids only cross-react ca. 0.8 and 2% with the antiserum, their levels were very high (400 to 1400 ng ml-’ cortisol). There appeared to be little or no 17,2O@P in the free fractions of the plasmas, but 299 0016~6480/90 $1.50

300 LEVELS

SCOTT,

OF STEROID

IMMUNOREACTIVITY

CANARIO,

AND

PRAT

TABLE 1 (ng ml-‘) IN DIETHYL OVULATING

FEMALE

ETHER BASS

EXTRACTS

OF PLASMAS

FROM

SIX

Female 1

2

3

4

5

6

1I-deoxycortisol Free Conjugated

12.0 13.4

13.2 13.3

9.7 9.6

16.7 8.6

14.5 8.6

11.2 8.1

17,2Op-P Free Conjugated

1.7 14.2

1.3 13.0

0.8 6.7

0.8 5.7

1.0 5.6

0.7 5.6

17,2Op,21-P Free Conjugated

4.6 14.5

4.8 13.7

3.0 8.5

3.3 6.7

3.5 6.7

3.1 7.2

0.9

1.8

1.3

0.7

0.8

0.9

Steroid

17-P Free 17@oestradiol Free

co.4

Radioimmunoassay of ovarian steroids in plasmas of ovulating female sea bass (Dicentrarchus labrax).

Radioimmunoassays of the free and conjugated fractions of plasmas from ovulating sea bass (Dicentrarchus labrax) have revealed the presence of several...
249KB Sizes 0 Downloads 0 Views