Here's some basic information found during a random search:
Glomerulonephritis is a lot more common than amyloidosis. Glomerulonephritis is inflammation of the glomeruli (the filtering structures of the kidney). It can occur secondary to many other illnesses, including many disease organisms (leptospirosis, Lyme disease, heartworms, brucellosis, hepatitis), cancer, pancreatitis, immune-mediated hemolytic anemia, hyperadrenocorticism and systemic lupus erythematosus and other immune mediated diseases. It can also occur as a primary, or idiopathic, illness. Sometimes finding and controlling the underlying problem can arrest the degenerative process and stop the progression of kidney failure. More often, once this problem starts it is slowly progressive over time.
There are treatments that can help with glomerulonephritis. As mentioned above, an effort should be made to find and treat any contributing condition. To help prevent protein loss and control high blood pressure associated with kidney failure, enalapril or other acetylcholinesterase (ACE) inhibitors may be helpful. The usual dosage of enalapril for this condition is 0.25 go 0.5mg/kg once or twice a day. Aspirin may help to prevent blood clotting that sometimes occurs due to glomerulonephritis. The dosage for aspirin therapy for this purpose is usually lower than for other conditions. A dosage for aspirin of 0.5 to 5mg/kg is enough to inhibit blood clotting. A low sodium, low total protein but very high quality protein diet, such as Purina NF or Hills k/d is helpful. Encouraging fluid intake is helpful. If the serum albumin level drops low enough to cause fluid accumulation in the abdomen it may be necessary to give diuretics. Calcitriol is more likely to provide a benefit in a patient with glomerulonephritis since this tends to be a more slowly progressing disease.
I would HIGHLY recommend contacting Dr. Rebecca Remillard at Angell Animal Medical Center, Boston, MA. She is absolutely top notch in canine nutrition and does telephone consultations. You must send her a complete history and test results in order for her to map out a diet specific to your needs.
As an aside to this whole discussion, I would cast my vote as a NO to a kidney biopsy. Having had one with ARF, even the internist treating my girl said that a he would only recommend a biopsy every other possible treatment had failed. Not something you want to do without a great deal of thought.