Hi Flo,
Missed you in chat!
If your blood pressure is high, it is likely that any endocrinologist / medical practicioner will want to treat the underlying reasons before prescribing HRT.
This may be due to a number of Physical or Neurological reasons (i.e Diabetes or stress) or because of existing medical conditions and treatments. Your Doctor should look at any contra-indications which exist bewteen existing medicines and proposed HRT.
Estrogen is indeed a chemical (or family of Chemicals) that can effect blood pressure, for example the Contraceptive Pill is well known for being a cause of high blood pressure / strokes in women.
I have known a few FTM friends who have had to stop HRT because of high blood pressure, but this is rare.
The main thing is to ensure that by starting HRT your health is not at risk and any good medical practitioner will tell you this.
Buffy