Innovative Research  (http://www.innovrsrch.com/product/productInfo.asp?name=DEOXYCORTICOSTERONE+ACETATE+(DOCA)) manufactures DOCA pellets that can be implanted subcutaneously or intraperitoneally. A 25 mg pellet will induce hypertension in the rat over 3 weeks. Please refer to some of my publications in which we used this mode of salt loading to induce hypertension. The pellets are quite expensive, but they are effective.I suppose it also depends on whether your animals are salt sensitive or resistant.  Good luck  

DOCA pellets can be implanted subcutaneously or intraperitoneally with the dose of 25 mg for 3 or 4 weeks.

You can dissolve DOCA in sesame oil and give a dose of 20 mg/kg ( or 10 mg per rat of 200 gm) on alternate days for 35 days. Also give 1% NaCl in drinking water. The weight of rat should not be more than 200 gm.

thanks a lot  for your  contribution