322
ECKART SCHOTT, MARTIN PAUL AND DETLEV GANTEN
Choice of strain
The development of transgenic mice is well established and the related techniques are well documented elsewhere ( 13 ). Since the development of transgenic rats is a relatively new procedure we will focus predominantly on this
species in the context of transgenic technology. Superovulation can be induced in mature and immature rats (20-23). The optimum age, for Superovulation varies between strains. The period immediately preceeding puberty is the best time to perform superovulation. In Sprague-Dawley rats this
is between day 29 and 31, andin Wistar Kyoto rats around day 33. This is in
contrast to mice where the optimum age to perform Superovulation is 4-6
weeks of age irrespective of the strain chosen.
Procedure
Superovulation
Superovulation is essential to obtain a sufficient number of oocytes with
normal developmental potential. Difficulties in inducing efficient Superovulation have long prevented the application of transgenic technology to
rats. In mice, a single dose of pregnant mare serum gonadotropin
(PMSG) is usually sufficient to induce superovulation. The use of PMSG
in rats, in contrast, is associated with a high variability in the ovulatory response (24, 25), a low fertilization rate, and a high percentage of degenerated
oocytes. Furthermore, oocytes do not develop normally (26). Since PMSG
e:xhibits both, follicle stimulating hormone (FSH) and luteinizing hormone
(LH) activity (20-23), the relatively high percentage ofLH activity in PMSG
is thought to be the reason for the low efficiency of superovulation in rats
after treatment with PMSG (10). High LH activity can induce an excessive
synthesis of androgens in the ovaries 36 hours after PMSG application,
which may cause degeneration of the oocytes (27).
A method to obtain large amounts of normally developed rat oocytes has
been developed by Armstrong and co-workers (28). Using highly purified
FSH preparations from the porcine pituitary, they showed that a specified
ratio ofLH/FSH for a given FSH amount is necessary to achieve appropriate
superovulation in the rat. Use of a minipump-system, which is implanted
subcutaneously, is necessary (28) because of the short half-life of purified
FSH (29, 30). According to the protocol of Armstrong et al. (28), a combination of lU FSH and 0.2 IU HCG per 24 hours is administered to immature
rats over a 72 h period. Fifty hours after implantation of the mini pump, 30
ECKART SCHOTT, MARTIN PAUL AND DETLEV GANTEN
Choice of strain
The development of transgenic mice is well established and the related techniques are well documented elsewhere ( 13 ). Since the development of transgenic rats is a relatively new procedure we will focus predominantly on this
species in the context of transgenic technology. Superovulation can be induced in mature and immature rats (20-23). The optimum age, for Superovulation varies between strains. The period immediately preceeding puberty is the best time to perform superovulation. In Sprague-Dawley rats this
is between day 29 and 31, andin Wistar Kyoto rats around day 33. This is in
contrast to mice where the optimum age to perform Superovulation is 4-6
weeks of age irrespective of the strain chosen.
Procedure
Superovulation
Superovulation is essential to obtain a sufficient number of oocytes with
normal developmental potential. Difficulties in inducing efficient Superovulation have long prevented the application of transgenic technology to
rats. In mice, a single dose of pregnant mare serum gonadotropin
(PMSG) is usually sufficient to induce superovulation. The use of PMSG
in rats, in contrast, is associated with a high variability in the ovulatory response (24, 25), a low fertilization rate, and a high percentage of degenerated
oocytes. Furthermore, oocytes do not develop normally (26). Since PMSG
e:xhibits both, follicle stimulating hormone (FSH) and luteinizing hormone
(LH) activity (20-23), the relatively high percentage ofLH activity in PMSG
is thought to be the reason for the low efficiency of superovulation in rats
after treatment with PMSG (10). High LH activity can induce an excessive
synthesis of androgens in the ovaries 36 hours after PMSG application,
which may cause degeneration of the oocytes (27).
A method to obtain large amounts of normally developed rat oocytes has
been developed by Armstrong and co-workers (28). Using highly purified
FSH preparations from the porcine pituitary, they showed that a specified
ratio ofLH/FSH for a given FSH amount is necessary to achieve appropriate
superovulation in the rat. Use of a minipump-system, which is implanted
subcutaneously, is necessary (28) because of the short half-life of purified
FSH (29, 30). According to the protocol of Armstrong et al. (28), a combination of lU FSH and 0.2 IU HCG per 24 hours is administered to immature
rats over a 72 h period. Fifty hours after implantation of the mini pump, 30